MCQ Questions

Answer: (c)
Explanation:

• Many of Harappan cities were divided into two or more parts. Usually, the part to the west was smaller but higher. Archaeologists describe this as the citadel
• Generally, the part to the east was larger but lower. This is called the lower town. Very often walls of baked brick were built around each part.
• The bricks were so well baked that they have lasted for thousands of years. The bricks were laid in an interlocking pattern and that made the walls strong.
• In some cities, special buildings were constructed on the citadel. For example, in Mohenjodaro, a very special tank, which archaeologists call the Great Bath, was built in this area.

Answer: (b)
Explanation:

• Houses were either one or two storeys high, with rooms built around a courtyard. Most houses had a separate bathing area, and some had wells to supply water.
• Many of these cities had covered drains. Very often, drains in houses were connected to those on the streets and smaller drains led into bigger ones.
• As the drains were covered, inspection holes were provided at intervals to clean them.
• All three-houses, drains and streets were probably planned and built at the same time.

Answer: (a)
Explanation:

• Cotton was probably grown at Mehrgarh about 7000 years ago. Actual pieces of cloth were found attached to the lid of a silver vase and some copper objects at Mohenjodaro.
• Archaeologists have also found spindle whorls, made of terracotta and faience. These were used to spin thread.

Answer: (c)
Explanation:

• The Harappans probably got copper from present-day Rajasthan, and even from Oman in West Asia.
• Tin, which was mixed with copper to produce bronze, may have been brought from present day Afghanistan and Iran.
• Gold could have come all the way from present-day Karnataka, and precious stones from present day Gujarat, Iran and Afghanistan.

Answer: (c)
Explanation:

• A new tool, the plough, was used to dig the earth for turning the soil and planting seeds. While real ploughs, which were probably made of wood, have not survived, toy models have been found.
• As this region does not receive heavy rainfall, some form of irrigation may have been used. This means that water was stored and supplied to the fields when the plants were growing.

Answer: (b)
Explanation:

• The city of Dholavira was located on Khadir Beyt (also spelled as Bet) in the Rann of Kutch, where there was fresh water and fertile soil.
• Unlike some of the other Harappan cities, which were divided into two parts, Dholavira was divided into three parts, and each part was surrounded with massive stone walls, with entrances through gateways. There was also a large open area in the settlement, where public ceremonies could be held.
• Other finds include large letters of the Harappan script that was carved out of white stone and perhaps inlaid in wood. This is a unique find as generally Harappan writing has been found on small objects such as seals.

Answer: (b)
Explanation:

• The city of Lothal stood beside a tributary of the Sabarmati, in Gujarat, close to the Gulf of Khambat.
• It was situated near areas where raw materials such as semi-precious stones were easily available.
• This was an important centre for making objects out of stone, shell and metal. There was also a store house in the city.
• Many seals and sealings (the impression of seals on clay) were found in this storehouse.

Answer: (a) About 4,700 years ago

Answer: (a) One or two storeys

Answer: (c) Both (a) and (b)

Answer: (d) All of these

Answer: (a) Gum

Answer: (c) Blue or sea green

Answer: (d) Rajasthan

Answer: (b) Farmers and herders

Answer: (b) stored water

Answer: (b) Dockyards

Answer: (a)
Explanation:
Archaeologists call the earliest period the Palaeolithic. This comes from two Greek words, ‘palaeo’, meaning old, and ‘lithos’, meaning stone. The name points to the importance of finds of stone tools. The Palaeolithic period extends from 2 million years ago to about 12,000 years ago. This long stretch of time is divided into the Lower, Middle and Upper Palaeolithic. This long span of time covers 99% of human history.

Answer: (c)
Explanation:
• The period when we find environmental changes, beginning about 12,000 years ago till about 10,000 years ago is called the Mesolithic (middle stone) age.
• Stone tools found during this period are generally tiny, and are called microliths.
• Microliths were probably stuck on to handles of bone or wood to make tools such as saws and sickles.
• At the same time, older varieties of tools continued to be in use.

Answer: (c)
Explanation:

• Around 12,000 years ago, there were major changes in the climate of the world, with a shift to relatively warm conditions. In many areas, this led to the development of grasslands. This in turn led to an increase in the number of deer, antelope, goat, sheep and cattle, i.e. animals that survived on grass.
• Those who hunted these animals now followed them, learning about their food habits and their breeding seasons. It is likely that this helped people to start thinking about herding and rearing these animals themselves. Fishing also became important.

Answer: (c)
Explanation:
Archaeologists have found traces of huts or houses at some sites. For instance, in Burzahom (in present-day Kashmir) people built pit-houses, which were dug into the ground, with steps leading into them. These may have provided shelter in cold weather. Archaeologists have also found cooking hearths both inside and outside the huts, which suggests that, depending on the weather, people could cook food either indoors or outdoors.

Answer: (c)
Explanation:

• Stone tools have been found from many sites as well. Many of these are different from the earlier Palaeolithic tools and that is why they are called Neolithic.
• These include tools that were polished to give a line cutting edge, and mortars and pestles were used for grinding grain and other plant produce.
• Mortars and pestles are used for grinding grain even today, several thousand years later.
• At the same time, tools of the Palaeolithic types continued to be made and used, and remember, some tools were also made of bone.

Answer: (d)
Explanation:

• Mehrgarh site is located in a fertile plain, near the Bolan Pass, which is one of the most important routes into Iran. Mehrgarh was probably one of the places where people learnt to grow barley and wheat, and rear sheep and goats for the first time in this area.
• It is one of the earliest villages that we know about. At this site many animal bones were found.
• Bones of wild animals such as the deer and pig, and also bones of sheep and goat were found.
• Other finds at Mehrgarh include remains of square or rectangular houses. Each house had four or more compartments, some of which may have been used for storage.
• When people died, their relatives and friends generally paid respect to them. People looked after them, perhaps in the belief that there is some form of life after death.
• Burial is one such arrangement. Several burial sites have been found at Mehrgarh. In one instance, the dead person was buried with goats, which were probably meant to serve as food in the next world.

Answer: (a)
Explanation:

Answer: (c) Fruits, vegetable and grains

Answer: (d) All of these

Answer: (c) Dog

Answer: (c) Both (a) and (b)

Answer: (c) Mehrgarh (Pakistan)

Answer: (a) Archaeologists

Answer: (c) Goat

Answer: (b) Scholars

Answer: (c) Pakistan

Answer: (a) to serve as food in next life

Answer: (a) About 12,000 years ago

Answer: (c)
Explanation:

• People have lived along the banks of Narmada river for several hundred thousand years. Some of the earliest people who lived here were skilled gatherers, that is, people who gathered their food. They knew about the vast wealth of plants in the surrounding forests, and collected roots, fruits and other forest produce for their food. They also hunted animals.
• Garo hills to the north-east and the Vindhyas in Central India were some of the areas where agriculture developed. The places where rice was first grown are to the north of the Vindhyas.
• Magadha lying in the state of Bihar, its rulers were very powerful and set up a large kingdom. Kingdoms were set up in other parts of the country as well.

Answer: (b) Narmada
Explanation:
We have seen that inscriptions are inscribed on hard surfaces. Many of these were inscribed sev¬eral hundreds of years ago. All inscriptions con¬tain both scripts and languages. Languages which were used, as well as scripts, have changed over time. Scholars understand through a pro¬cess known as decipherment.

Answer: (b) Narmada

Answer: (a) Ganga

Answer: (a) Magadha

Answer: (c) Both (a) and (b)

Answer: (a) North west

Answer: (a) On palm leaf

Answer: (a) In temples and monastaries

Answer: (a) Who study past

Answer: (d) All of these

Answer: (a) Archaeology

Answer: (c) 8000 years ago

Answer: (d) All of these

Answer: (a) Sanskrit

Answer: (d)
Explanation:
Here, all the options are correct because idli is pre-pared by rice, for preparing kheer, sugar is needed and chicken curry cannot be prepared without water.

Answer: (d)
Explanation:
Animals which eat only plants or plant products are called herbivores. There are some animals which eat other animals. These animals are called carnivores. Some animals which eat both plants and animals. These are called omnivores.

Answer: (c)
Explanation:
The ingredients contain some components that sire needed by our body. These components are called nutrients. The major nutrients in our food are named carbohydrates, proteins, fats, vitamins and minerals. In addition, food contains dietary fibres and water which Eire Also needed by our body. The main carbohydrates found in our food are in the form of starch and sugars.

Answer: (a)
Explanation:
The main carbohydrates found in our food are in the form of starch Eind sugars. Take a small quantity of a food item or a raw ingredient. Put 2-3 drops of dilute iodine solution on it. A blue-black colour indicates that it contains starch. Add two drops of solution of copper sulphate and ten drops of solution of caustic soda to the test tube. A violet colour indicates presence of proteins in the food item. An oily patch on paper shows that the food item contains fat. The food items may sometimes contain a little water too.

Answer: (d)
Explanation:
Carbohydrates mainly provide energy to our body. Fats also give us energy. In fact, fats give much more energy as compared to the same amount of carbohydrates. The food containing fats and car-bohydrates are also called ‘energy-giving foods’. Proteins are needed for the growth and repair of our body. Vitamins help in protecting our body against diseases. VitEimins also help in keeping our eyes, bones, teeth and gums healthy. Minerals Eire needed by our body in small amounts. Each one is essentiEd for proper growth of our body and to maintain good health.

Answer: (d)
Explanation:
The sources of carbohydrates are sweet potato, sugarcane, wheat, rice, bajra, melon, mango, potato, maize, meat, fish, egg, milk, ghee, etc. The sources of proteins are- gram, moong, tuar dal, beans, meat, eggs, fish, peas, soyabeans, paneer etc. The sources of vitamins are-milk, eggs, spinach, apple etc. The sources of vitamins are- papaya carrot mango, guava, lemon, amla etc.

Answer: (a)
Explanation:
Vitamins help in protecting our body against dis-eases. Vitamins also help in keeping our eyes, bones, teeth and gums healthy. Vitamins are of different kinds known by different names. Some of these are Vitamin A, Vitamin C, Vitamin D, Vitamin E and K. There is also a group of vitamins called Vitamin B-complex. Our body needs all types of vitamins in small quantities. Vitamin A keeps our skin and eyes healthy. Vitamin C helps body to fight against many diseases. Vitamin D helps our body to use calcium for bones and teeth.

Answer: (c)
Explanation:
Dietary fibres are also known as roughage. Roughage is mainly provided by plant products in our foods. Whole grains and pulses, potatoes, fresh fruits and vegetables are main sources of roughage. Roughage does not provide any nutrient to our body, but is an essential component of our food and adds to its bulk. This helps our body get rid of undigested food.

Answer: (a)
Explanation:

Answer: (a)
Explanation:
The thin strands of thread that are made up of still thinner strands called fibres. Fabrics are made up of yams and yams are further made up of fibres. The fibres of some fabrics such as cotton, jute, silk and wool are obtained from plants and animals. These are called natural fibres.

Answer: (d)
Explanation:
Cotton and jute are examples of fibres obtained from plants. Wool and silk fibres are obtained from animals. Wool is obtained from the fleece of sheep or goat. It is also obtained from the hair of rabbits, yak and camels. Silk fibre is drawn from the cocoon of silkworms.

Answer: (d)
Explanation:
The fruits of the cotton plant (cotton bolls) are about the size of a lemon. After maturing, the bolls burst open and the seeds covered with cotton fibres can be seen. From these bolls, cotton is usually picked by hand. Fibres are then separated from the seeds by combing. This process is called ginning of cotton. Ginning was traditionally done by hand. The process of making yam from fibres is called spinning. In this process, fibres from a mass of cotton wool are drawn out and twisted. This brings the fibres together to form a yam. The process of arranging two sets of yams together to make a fabric is called weaving.

Answer: (a)
Explanation:
Plants with green and tender stems are called herbs. They are usually short and may not have many branches.

Answer: (a)
Explanation:
Some plants develop branches near the base of the stem. The stem is hard but not very thick. Such plants are called shrubs.

Answer: (c)
Explanation:
Some plants are very tall and have hard and thick stem. The stems have branches in the upper part, much above the ground. Such plants are called trees.

Answer: (a)
Explanation:
The part of leaf by which it is attached to the stem is called petiole. The broad, green part of the leaf is called lamina. The lines on the leaf are called veins. A prominent line in the middle of the leaf is called the midrib. The design made by veins in a leaf is called the leaf venation. If this design is net-like on both sides of midrib, the venation is reticulate.

Answer: (c)
Explanation:
The main root is called tap root and the smellier roots are called lateral roots. Plants with roots do not have a main root. All roots seem similar and these are called fibrous roots. The innermost part of flower is called the pistil. Some small bead like structures inside the ovary are called ovules.

Answer: (c)
Explanation:
Fish have slippery scales on their bodies. These scales protect the fish and also help in easy move-ment through water. Fish have flat fins and tails that help them to change directions and keep their body balanced in water. Gills present in the fish help them to use oxygen dissolved in water.

Answer: (a)
Explanation:
The place where organisms live is called habitat. Habitat means a dwelling place (a home). The habitat provides food, water, air, shelter and other needs to organisms. Several kinds of plants and animals live in the same habitat. The plants and animals that live on land are said to live in terrestrial habitats. Some examples of terrestrial habitats are forests, grasslands, deserts, coastal and mountain regions. On the other hand, the habitats of plants and animals that live in water are called aquatic habitats. Lakes, rivers and oceans are some examples of aquatic habitats. There are large variations among terrestrial habitats like forests, grasslands, deserts, coastal and mountain regions located in different parts of the world.

Answer: (b)
Explanation:
Adaptation does not take place in a short time because the abiotic factors of a region also change very slowly. Those organisms which cannot adapt to these changes die, and only the adapted ones survive. Organisms adapt to different abiotic factors in different ways. This results in a wide variety of organisms in different habitats.

Answer: (a)
Explanation:
Desert plants lose very little water through tran-spiration. The leaves in desert plants are either absent, very small, or they are in the form of spines. This helps in reducing loss of water from the leaves through transpiration. The leaf-like structure you see in a cactus is, in fact, its stem. Photosynthesis in these plants is usually carried out by the stems.

Answer: (b)
Explanation:
The trees are normally cone-shaped and have sloping branches. The leaves of some of these trees are needle-like. This helps the rainwater and snow to slide off easily. There could be trees with shapes very different from these that are also present on mountains. They may have different kinds of adaptations to survive on the mountains. Animals living in the mountain regions are also adapted to the conditions there. They have thick skin or fur to protect them from cold. For example, yaks have long hair to keep them warm. The snow leopard has thick fur on its body including feet and toes. This protects its feet from the cold when it walks on the snow. The mountain goat has strong hooves for running up the rocky slopes of the mountains.

Answer: (a)
Explanation:
The organisms, both plants and animals, living in a habitat are its biotic components. The nonliving things such as rocks, soil, air and water in the habitat constitute its abiotic components. A deer is a animal that lives in forests and grasslands. It has strong teeth for chewing hard plant stems of the forest. A deer needs to know about the presence of predators (animals like lion that make it their prey) in order to run away from them and not become their prey. Lions light brown colour helps it to hide in diy grasslands when it hunts for prey (animals to eat).

Answer: (c)
Explanation:
One way of increasing the availability of water is to collect rainwater and store it for later use. Collecting rainwater in this way is called rainwater harvesting. The basic idea behind rainwater harvesting is “Catch water where it falls”. Two techniques of rainwater harvesting are-
1. Rooftop rainwater harvesting: In this system, the rainwater is collected from the rooftop to a storage tank, through pipes. This water may contain soil from the roof and need filtering before it is used. Instead of collecting rainwater in the tank, the pipes can go directly into a pit in the ground. This then seeps into the soil to recharge or refill the groundwater.
2. Another option is to allow water to go into the ground directly from the roadside drains that collect rainwater.

Answer: (a)
Explanation:
The process of condensation plays an important role in bringing water back to the surface of earth. As we go higher from the surface of the earth, it gets cooler. When the air moves up, it gets cooler and cooler. At sufficient heights, the air becomes so cool that the water vapour present in it condenses to form tiny drops of water called droplets. It is these tiny droplets that remain floating in air and appear to us as clouds. It so happens that many droplets of water come together to form larger sized drops of water. Some drops of water become so heavy that they begin to fall. These falling water-drops are, what we call rain. In special conditions, it may also fall as hail or snow.

Answer: (c)
Explanation:
When air comes in contact with a cool surface, it condenses and drops of water appear on the cooled surfaces. The presence of water vapour in air is important for the water cycle in nature. The presence of some components in the air, do not support burning. The major part of air (which does not support burning candle) is nitrogen. The burning of fuel also produces smoke. Smoke contains a few gases and fine dust particles and is often harmful. That is why you see long chimneys in factories.

Answer: (b)
Explanation:
By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% Argon, 0.04% carbon di-oxide and small amount of other gases. Air also contains variable amount of water vapour, on av-erage around 1% at sealevel and 0.4% over the entire atmosphere.

Answer: (c)
Explanation:
The wind makes the windmill rotate. The windmill is used to draw water from tubewells and to run flour mills. Windmills are also used to generate electricity. Air helps in the movement of sailing yachts, gliders, parachutes and aeroplanes. Birds, bats and insects can fly due to the presence of air. Air also helps in the dispersal of seeds and pollen of flowers of several plants. Air plays an important role in water cycle.

Answer: (c)
Explanation:
The method of preparing compost with the help of redworms is called vermi composting. Redworms do not have teeth. They have a structure called ‘gizzard’, which helps them in grinding their food. Redworms do not survive in very hot or very cold surroundings. They also need moisture around them.

Answer: (d)
Explanation:
The joint where our neck joins the head is a pivotal joint. It allows us to bend our head forward and backwards and turn the head to our right or left. The elbow has a hinge joint that allows only a back and forth movement. The bones cannot move at these joints. Such joints are called fixed joints.

Answer: (c)
Explanation:
A mixture is made up two or more substances. The pure substances which sire present in a mixture are called components of the mixture (or constituents of the mixture). The components of a mixture retain their original properties. So, a mixture shows the properties of all substances present in it. A mixture can be solid, liquid or gas. For example, soil is a solid mixture, milk is a liquid mixture whereas air is a gaseous mixture. In some cases we can easily see the different substances (or components) present in mixture.

Answer: (b)
Explanation:
Threshing is the process in which stalks (of wheat, paddy, etc.) are beaten to separate grains from stalks, and the chaff that covers the grains. The method of separation is based on the fact that the ‘stalks’ of the crop plants and the ‘chaff are soft materials whereas the grains themselves are very hard. Winnowing is the method of separating husk from grains with the help of wind. This method is based on the fact that husk is very light whereas wheat grains are comparatively heavy. Hand-picking means to take out by hand. The method of hand-picking is used to separate those substances where one of the components is in small quantify. The method of hand-picking is used to separate undesirable substances such as small pieces of stones from wheat, rice and pulses. Sieving is used to separate those solid mixtures which have components of different sizes.

Answer: (a)
Explanation:
A given quantity of water can dtssolve only a certain maximum amount of a substance (at particular temperature). A solution in which no more substance can be dissolved at that temperature, is called a saturated substance. A saturated solution contains the maximum amount of substance which can be dissolved in it at a given temperature. The solubility of a substance refers to its saturated solution.

Answer: (c)
Explanation:
Distillation is the process of heating water to form water vapour, and then cooling water vapour (steam) to get back liquid water. The changing of water into water vapour on heating, is called evaporation (or boiling). And the changing back of hot water vapour (or steam) into liquid water on cooling, is called condensation. Thus distillation involves two processes: evaporation (or boiling) followed by condensation.

Answer: (c)
Explanation:
A change which can be reversed to form the original substance is called a reversible change. When ice changes into water, then there is a change from solid state to liquid state. And when water changes into steam, then there is a change from liquid state to gaseous state. So, in general we can say that: change of state is a reversible change.

Answer: (b)
Explanation:
A change which cannot be reversed to form the original substance (or substances) is called an irreversible change. A very small quantity of curd is added to warm milk. It is kept aside for few hours. During this time, milk changes into curd. This curd cannot be changed back into milk by any means. So, it is a irreversible change. The flour cannot be converted back into wheat grains. So, the grinding of wheat to form flour is an irreversible change. The cooked food cannot be converted back into raw food materials. So, cooking is an irreversible change. The increase of size on heating is called expansion. It is called reversible change because when the hot object is cooled, it decreases in size and comes back to the original size.

Answer: (c)
Explanation:
We classify the objects because it gives us the following advantages:
(i) The classification of objects into groups makes it easier to locate them and work with them.
(ii) The classification of objects into groups helps in understanding them. This is because if we know properties of one member of group, we can get an idea of the properties of the other members of the group.

Answer: (b)
Explanation:
The classification of the various objects can be done on the basis of their similarities or dissimilarities. The materials are classified on the basis of property such as appearance, hardness, solubility, heaviness or lightness with respect to water transparency, translucency or opaqueness, use, colour, shape, size, texture, etc.

Answer: (a)
Explanation:
The word ‘acid’ is derived from the Latin word ‘acidus’ which means ‘sour’. The acids which occur in fruits and vegetables, etc. are called naturally-occurring acids. The naturally-occurring acids are weak acids. These acids are also called organic acids. The acids obtained from minerals are called mineral acids. Mineral acids are called inorganic acids. The bases which are soluble in water are called alkalis.

Answer: (b)

Answer: (a)
Explanation:
Some important uses of acid are:

• Hydrochloric acid for cleaning tiles, toilets; for the preparation of chlorides and chlorine gas; for cleaning iron sheets before galvanization: for extracting glue from bones; In textile industry for dyeing.
• Nitric acid for preparing fertilizers, explosives and drugs; in for refining of gold and silver.
• Sulphuric acid for preparing fertilizers, detergents, plastics, synthetic fibres; in petroleum industry for refining; in cleaning metal surfaces before electroplating.

Answer: (a)
Explanation:
Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. The indicators change their colour when added to a solution containing an acidic or a basic substance. The most commonly used natural indicator is litmus. It is extracted from lichens. When added to . an acidic solution, it turns red and when added to a basic solution, it turns blue. Turmeric is yellow in neutral solutions, yellow in acidic solutions and red in basic solutions. China rose indicator in water is pink, magenta in acidic solution and green in basic solution.

Answer: (b)
Explanation:
When an acidic solution is mixed with a basic solution, both the solutions neutralise the effect of each other. When an acid solution and a base solution are mixed in suitable amounts, both the acidic nature of the acid and the basic nature of the base are destroyed. The resulting solution is neither acidic nor basic. The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat. Acid+Base-> Salt+Water (Heat is evolved). Heat is evolved; therefore, it is an exothermic reaction.

Answer: (b)
Explanation:
Dissolution is a process by which any solute gets dissolved in a solvent. Exothermic reactions are those reactions during which heat is evolved. Endothermic reaction is that reaction during which heat is absorbed. The change which can be reversed by reversing the conditions is called reversible change. Example—glowing of a bulb.

Answer: (a)
Explanation:
Properties such as shape, size, colour and state of a substance are called its physical properties. A change in which a substance undergoes a change in its physical properties is called a physical change. A physical change is generally reversible. In such a change no new substance is formed. Physical changes are temporary and reversible. No or very small amount of energy is either absorbed or evolved during a physical change.

Answer: (c)
Explanation:
A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction. Chemical changes are very important in our lives. All new substances are formed as a result of chemical changes. For example, digestion of food in our body, ripening of fruits, fermentation of grapes, etc., happen due to series of chemical changes. A change in which a substance undergoes a change in its physical properties is called a physical change.. During sublimation, a solid substance when heated changes into vapour form, and the vapour on cooling gives back the substance in solid form.

Answer: (b)
Explanation:
The process of rusting can be represented by the following equation: Iron (Fe) + Oxygen (02, from the air) + water (H₂O) => rust (iron oxide Fe₂O₃ ) For rusting, the presence of both oxygen and water (or water vapour) is essential. In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster. This process of depositing a layer of zinc on iron is called galvanisation. The iron pipes we use in our homes to carry water are galvanised to prevent rusting, painting, greasing, oiling, tinning and cathodic protection can be used to prevent rusting of iron.

Answer: (c)
Explanation:
The salt obtained in this manner is not pure and the shape of its crystals cannot be seen clearly. However, large crystals of pure substances can be formed from their solutions. Such a process is called crystallisation. It is an example of a physical change.

Answer: (b)
Explanation:
The short-time atmospheric conditions at a particular place and time with respect to temperature, relative humidity, rainfall, wind speed, etc. is called the weather at that place. The temperature, humidity, rainfall, wind speed, etc. are called elements of weather. The science of the study of weather is called meteorology

Answer: (c)
Explanation:
Weather forecast is based on the data collected by weather balloons,satellite, photographs of the cloud formation etc. Weather forecasting is helpful to people in the following ways:
1. It allows people to prepare for bad weather.
2. It helps in the planning of daily activities.

Answer: (b)
Explanation:
The records of the weather have been preserved for the past several decades. These help us to determine the weather pattern at a place. The average weather pattern taken over a long time, say 25 years, is called the climate of the place. The annual record of long term average temperature and rainfall at a particular place is called climate chart.

Answer: (d)
Explanation:
The sea affects the climate. Coastal areas are cooler and wetter than the inland areas. Warm ocean currents make the climate warm and wet. The direction of the prevailing winds from the sea/ocean side bring rain to coastal areas and dry weather to inland areas. Mountains receive more rainfall than low lying areas because the temperature on top of mountains is lower than sea level. The distance from the equator affects the climate of a place. The equator receives the more sunlight than anywhere else on the earth.

Answer: (a)
Explanation:
Animals are adapted to survive m the conditions in which they live. Animals living in very cold and hot climate must possess special features to protect themselves against the extreme cold or heat. Adaption is of two types- permanent- has a genetic basis and it causes permanent changes in the individuals: temporary- is a short term adaptation and is not inherited.

Answer: (d)
Explanation:
The lion-tailed macaque (also called Beard ape) lives in the rainforests of Western Ghats. Its most outstanding feature is the silver-white mane, which surrounds the head from the cheeks down to its chin. Many animals are adapted to living on the trees (arboreal). Red-eyed frog has developed sticky pads on its feet to help it climb trees on which it lives. To help them live on the trees, monkeys have long tails for grasping branches.

Answer: (a)
Explanation:
The main layers of the atmosphere are: Troposphere—most of the atmospheric air is present in troposphere. Clouds, rain and snow are seen in troposphere.
Stratosphere- there is very little water vapour. Supersonic aircraft fly in this layer. Ozone layer lies in central zone of stratosphere. Thermosphere-temperature increases with altitude.

Answer: (a)
Explanation:
The pressure exerted by air at any point on the earth is called atmospheric pressure. Air pressure is important for the following reasons:

1. It creates winds: when air moves, it becomes wind. The difference in atmospheric pressure gives rise to the wind system of the earth.
2. It influences weather: changes in weather are related to changes in atmospheric pressure.
3. Weather forecasting: changes in air pressure give important clues for forecasting weather.

Answer: (b)
Explanation:
Blowing or moving air is called wind. The speed of wind may vary from 5-10 km/h (gentle breeze) to 700-800 km/h (tornado). The speed and direction of wind is affected by the following factors : Location on the earth Rotation of the earth Local conditions Height from the ground

Answer: (d)
Explanation:
Thunderstorms develop in hot and humid tropical regions. Formation of a thunderstorm requires the following:

• Moisture
• Rapidly rising warm air
• Sea breeze or mountains

The swift movement of the falling water along with rising warm air, producing sound, lightning, heavy rain, and strong wind is called thunderstorm.

Answer: (c)
Explanation:
A small low-pressure system with very high speed winds revolving around it is called cyclone. The high speed winds revolve in anti-clock-wise direction in Northern Hemisphere and in clockwise direction in the Southern Hemisphere. Factors like wind speed, wind direction, temperature and humidity contribute to the development of cyclones. The centre of a cyclone is a calm area. It is called the eye of the cyclone. Cyclones that develop in the tropical region are different from those in the temperate latitudes. In general, tropical cyclones are more powerful than temperate cyclones.

Answer: (a)
Explanation:
Polymer-long chain-like molecule consisting of a large number of molecules joined to each other by chemical bonds.
Non biodegradable- substances which do not decompose to harmless substances by the action of air, water and bacteria.
Synthetic fibre- man-made fibres from simple, small molecules.

Answer: (a)
Explanation:
A long chain-like unit consisting of a large number of smaller molecules joined to each other by chemical bonds is called a polymer. The smaller molecules which combine to form the chain of a polymer are called monomers. The polymers which occur in nature are called natural polymers. For example, cellulose, silk, wool, proteins, etc. are natural polymers. The polymers which are made in laboratories factories from small molecules are called man-made (or synthetic) polymers. For example, nylon, polythene, polyvinyl chloride, rayon and teflon are some synthetic polymers.

Answer: (a)
Explanation:
Rayon is used—

• in the textile industry for making fabrics;
• in the manufacture of carpets;
• for the manufacture of tyre cord;
•  for making bandages and surgical dressings. Nylon is used—
• for the manufacture of iyre cords, fabrics and ropes;
• for making fishing nets and parachute ropes;
• for fabricating sheets, bristles for brushes, for making sarees, socks, neckties;
•  for making elastic hosiery;
• for making machine parts.

Polyester is used-

• for manufacturing sarees, dress materials, curtain cloth, etc.
• for making blends with other fibres; eg. grylene with cotton gives terycot, with wool it gives teiywool. Clothes made from blends are more comfortable to wear.
• for making sails for sail boats;
•  for making water hoses for fire fighting;
• for making conveyor belts.

Answer: (c)
Explanation:
Some of the characteristic properties of synthetic fibres are :

• Synthetic fibre does not get wet. So, the fabrics made from synthetic fibres dry up quickly.
• Synthetic fibres cure durable i.e, fabrics made from synthetic fibres last long.
• Synthetic fibres can be drawn to very fine thickness. So these are light-weight. As a result, the fabrics made from synthetic fibres are thin and hence light-weight.
• Synthetic fibres are strong, have high tensile strength and are abrasion-resistant. As a result, the fabrics made from synthetic fibres are long lasting and easy to maintain.
• Synthetic fibres are cheaper.

Answer: (b)
Explanation;
1. Thermoplastics are long chain polymers with
no cross-linking. Heating also does not produce any cross-linking between the chains
2. Thermoplastics can be processed repeatedly Example : Polythene, PVC, Polystyrene, Nylon, Polyesters, etc.

Answer: (d)
Explanation:
Polythene (or polyethylene) is obtained from ethylene under high temperature, high pressure and in the presence of a catalyst. Polythene is a thermoplastic polymer. So, it can be moulded into any shape and any number of times. Bakelite is a thermosetting plastic. Once set into a shape, bakelite does not melt/soften and retains its shape. Bakelite is obtained by reacting phenol with formaldehyde in the presence of a catalyst Melamine is also a thermosetting polymer. It is hard and a high polish polymer. Melamine is used for making unbreakable dinner-ware, and decorative objects rative objects.

Answer: (b)
Explanation:
Metals: Iron, Copper, Gold, Silver, Aluminium, Zinc, Lead are some commonly used metals.
Non-metals: Hydrogen, Oxygen, Nitrogen, Carbon, Sulphur, Phosphorus, Chlorine, Bromine, Iodine are commonly used non-metals
Metalloids: Boron, Silicon, Arsenic and Germanium are some metalloids.

Answer: (b)
Explanation:
1. Physical state: Under normal pressure, all metals except mercury are solid at room temperature. Mercury is liquid at room temperature.
2. Colour : Most metals except gold and copper are silvery grey in colour. Copper is reddish-brown and gold is golden yellow.
3. Appearance : All metals are shiny. The characteristic shine of metals is called metallic lustre. Thus, all metals have metallic lustre. Metals can be easily polished.
4. Hardness : Most metals are hard except sodium and potassium. Sodium and potassium metals can be easily cut with a knife. Osmium is hard enough to scratch glass.

Answer: (c)
Explanation:
Graphite is the only non-metal which conducts heat and electricity. Caesium metal have low melting point that it melts even when kept on palm. Diamond is the hardest substance known on earth.

Answer: (b)
Explanation:
The reactivity series of metals is an arrangement of metals in vertical column in order of decreasing reactivity The reactivity series is also called activity series of metals. In the activity series, the most reactive metal is placed at the top whereas the least reactive metal is placed at the bottom. The more reactive metal has greater tendency to form compounds. So, such metals are found only in the form of their compounds. Less reactive metals such as silver, gold and platinum are found in the free state in the earth’s crust.

Answer: (a)
Explanation:
Sulphur is used in manufacture of gun powder, sulphuric acid, in vulcanization of rubber. Phosphorus is used for the manufacture of match sticks, rat poison, phosphoric acid and fertilizers. Oxygen is supporter of combustion and used for respiration by living organisms. Hydrogen is used as a fuel, for manufacturing ammonia, hydrogen chloride, vegetable ghee by hydrogenation of oils. Chlorine is used for bleaching and sterilizing water.

Answer: (c)
Explanation:
Characteristics of particles of matter:

1. Particles of matter have space between them.
2. Matter is made up of particles.
3. Particles of matter are continuously moving.
4. Particles of matter attract each other.

Answer: (a)
Explanation:
On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

Answer: (a)
Explanation:
The word latent means hidden. The amount of heat energy that is required to change 1 kg. of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at 0°C (273 K) have more energy as compared to particles in ice at the same temperature.

Answer: (a)
Explanation:
A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition. Applying pressure and reducing temperature can liquefy gases, dry ice, etc. Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

Answer: (c)
Explanation:
The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation. The rate of evaporation increases with-

• an increase of surface area: If the surface area is increased, the rate of evaporation increases.
• an increase of temperature: With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.
• a decrease in humidity: Humidity is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is al-ready high, the rate of evaporation decreases.
• an increase in wind speed: It is a common observation that clothes dry faster on a windy day. With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.

Answer: (b)
Explanation:
Matter is made up of small particles. The matter around us exists in three states- solid, liquid and gas. The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases. The space in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.

Answer: (c)
Explanation:
Mixtures are constituted by more than one kind of pure form of matter. Alloys are mixtures of two or more metals or a metal and a non-metal and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper.

Answer: (b)
Explanation:
A solution is a homogeneous mixture of two or more substances. You come across various types of solutions in your daily life. Lemonade, soda water, etc. are all examples of solutions. Usually we think of a solution as a liquid that contains either a solid, liquid or a gas dissolved in it. But, we can also have solid solutions (alloys) and gaseous solutions (air). In a solution there is homogeneity at the particle level.

Answer: (a)
Explanation:
A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute. A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent.

Answer: (a)
Explanation:
A colloid is a heterogeneous mixture.

• The size of particles of a colloid is too small to be individually seen by naked eyes.
• Colloids are big enough to scatter a beam of light passing through it and make its path visible.
• They do not settle down when left undisturbed, that is, a colloid is quite stable.

Answer: (d)
Explanation:
The components of a colloidal solution are the dispersed phase and the dispersion medium. The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. Examples of Aerosol : fog, clouds, mist.

Answer: (c)
Explanation:
Ink is a mixture of a dye in water. Thus, we can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation. Cream from milk is separated by centrifugation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. The principle is that immiscible liquids separate out in layers depending on their densities using separating funnel.

Answer: (a)
Explanation:
Robert Boyle was the first scientist to use the term element in 1661. Antoine Laurent Lavoisier (1743-94), a French chemist, was the first to establish an experimentally useful definition of an ‘element’. He defined an ‘element’ as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. Elements can be normally divided into metals, non-metals and metalloids.

Answer: (a)
Explanation:
1. Elements react to form new compounds,
2. The composition of each new substance is al’ ways fixed.
3. The new substance has totally different con; stituent substances and properties.
4. The constituents can be separated only by chemical or electrochemical reactions.

Answer: (c)
Explanation:
According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is | composed of small particles called atoms. The postulates of this theory may be stated as follows:
(i) All matter is made up of very tiny particles , called atoms, which participate in chemical reactions.
(ii) Atoms are indivisible particles, which can not be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses and chemical properties.
(v) Atoms combine in the ratio of small whole numbers to form compounds.
(vi) The relative number and kinds of atoms are constant in a given compound.

Answer: (b)
Explanation:
Lavoisier, along with other scientists, noted that many compounds were composed of two or more elements and each such compound had the same elements in the same proportions, irrespective of where the compound came from or who prepared it. This law was stated by Proust as “In a chemical substance the elements are always present in definite proportions by mass”.

Answer: (b)
Explanation:
The most remarkable concept that Dalton’s atomic theoiy proposed was that of the atomic mass. According to him, each element had a characteristic atomic mass. The theory could explain the law of constant proportions so well that scientists were prompted to measure the atomic mass of an atom.

Answer: (a)
Explanation:
A molecule is, in general, a group of two or more atoms that are chemically bonded together, that is, tightly held together by attractive forces. A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. Atoms of the same element or of different elements can join together to form molecules.

Answer: (c)
Explanation:

Answer: (c)
Explanation:
Compounds composed of metals and non-metals contain charged species. The charged species are known as ions. Ions may consist of a single charged atom or a group of atoms that have a net charge on them. An ion can be negatively or positively charged. A negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’. A group of atoms carrying a charge is known as a polyatomic ion.

Answer: (c)
Explanation:
It was known by 1900 that the atom was indivisible particle but contained at least one subatomic particle – the electron identified by J.J. Thomson. Even before the electron was identified, E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. James Chadwick discovered neutron.

Answer: (a)
Explanation:
Thomson proposed that:
(i) An atom consists of a positively charged sphere and the electrons are embedded in it.
(ii) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral. Although Thomson’s model explained that atoms are electrically neutral.

Answer: (a)
Explanation:
In the experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil.

• He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.
• α-particles are doubly-charged helium ions. Since they have a mass of 4 u, the fast-moving α-particles have a considerable amount of energy.
• It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect to see large deflections.

The following observations were made:
(i) Most of the fast moving a-particles passed straight through the gold foil.
(ii) Some of the a-particles were deflected by the foil by small angles.
(iii) Surprisingly one out of every 12000 particles appeared to rebound.

Answer: (b)
Explanation:
The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury. The following rules are followed for writing the number of electrons in different energy levels or shells:
(i) The maximum number of electrons present in a shell is given by the formula (2n)2 , where ‘n’ is the orbit number or energy level index.
(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.
(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is, the shells are filled in a step wise manner.

Answer: (c)
Explanation:

Answer: (c)
Explanation:
Atomic number is the number of protons of an atom, which determines its atomic number. It is denoted by ‘Z’. the atomic number is defined as the total number of protons present in the nucleus of an atom, the mass of an atom resides in its nucleus. The mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom. It is denoted by A’. Isotopes are defined as the atoms of the same element, having the same atomic number but different mass numbers. Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars.

Answer: (d)
Explanation :
We can say that any of the following observations helps us to determine whether a chemical reaction has taken place or not :

1. Change in state
2. Change in colour
3. Evolution of a gas
4. Change in temperature.

As we observe the changes around us, we can see that there are many chemical reactions taking

Answer: (a)
Explanation:
The description of a chemical reaction in a sentence form is quite long. It can be written in a shorter form. The simplest way to do this is to write it in the form of a word equation. The substances that undergo chemical change in the reaction are the reactants. The new substance is formed during the reaction, is a product.

Answer: (a)
Explanation:
The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations.

Answer: (b)
Explanation:
To make a chemical equation more informative, the physical state of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (1), (aq) and (s), respectively. The word aqueous (aq) is written if the reactant or product is present as a solution in water.

Answer: (d)
Explanation:
A reaction in which a single product is formed from two or more reactants is known as a combination reaction. A large amount of heat is evolved. This makes the reaction mixture warm. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions. When a single reactant breaks down to give simpler products, it is a decomposition reaction. When a decomposition reaction is carried out by heating, it is called thermal decomposition. In displacement reaction, the higher reactive metal displaces the less reactive metal.

Answer: (b)
Explanation:
Reactions also involve the gain or loss of oxygen or hydrogen by substances. Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen. Lead is losing oxygen, it is getting reduced. Carbon is gaining oxygen: it is getting oxidised.

Answer: (a)
Explanation:
Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator. When the litmus solution is neither acidic nor basic, its colour is purple.

Answer: (b)
Explanation:
There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators. Olfactory indicators can be used in the laboratory to test whether a solution is abase or an acid, a process called olfactory titration. Onion, clove oil and vanilla extract are examples of olfactory indicators.

Answer: (b)
Explanation:
The metal displaces hydrogen atoms from the adds as hydrogen gas and forms a compound called a salt. Thus, the reaction of a metal with an acid can be summarised as – Acid + Metal → Salt + Hydrogen gas. All metal carbonates and hydrogen carbonates react with acids to give a corre-sponding salt, carbon dioxide and water. Thus, the reaction can be summarised as-
Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water
The general reaction between a metal oxide and an acid can be written as – Metal oxide + Acid → Salt + Water.

Answer: (a)
Explanation:
The process of dissolving an acid or a base in water is a highly exothermic one. The acid must always be added slowly to water with constant, stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause bums.

Answer: (b)
Explanation:
A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline). pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value. The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH- ion concentration in the solution, that is, increase in the strength of alkali.

Answer: (c)
Explanation:
Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult. Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating.

Answer: (a)
Explanation:
The salt formed by the combination of hydrochloric acid and sodium hydroxide solution is called sodium chloride. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed- chlor for chlorine and alkali for sodium hydroxide.

Answer: (d)
Explanation:
Uses of washing soda (i) Sodium carbonate (washing soda) is used in glass, soap and paper industries, (ii) It is used in the manufacture of sodium compounds such as borax, (iii) Sodium carbonate can be used as a cleaning agent for domestic purposes, (iv) It is used for removing permanent hardness of water. For making baking powder, which is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. Bleaching powder is used – (i) for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry; (ii) as an oxidising agent in many chemical industries; and (iii) to make drinking water free from germs.

Answer: (b)
Explanation:
The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal. Metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat. The non-metals are either solids or gases except bromine which is a liquid. The ability of metals to be drawn into . sheets is called malleability.

Answer: (c)
Explanation:
All metals except mercury exist as solids at room temperature. Iodine is a non-metal but it is lustrous. Carbon is a non-metal that can exist in different forms. Each form is called an allotrope. Diamond, an allotrope of carbon, is the hardest atural substance known and has a very high melting and boiling point. Graphite, another al- lotrope of carbon, is a conductor of electricity. Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

Answer: (c)
Explanation:
Metal react with oxygen to form metal oxide. Metallic oxides are mostly basic. Metals lose electrons to form positive ions. Metals are good reducing agents. More reactive metals can displace less reactive metals from its salt solution.

Answer: (a)
Explanation:
Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.

Answer: (d)
Explanation:
Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire. Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. Metals like aluminium, iron and zinc do not react either with cold or hot water. But, they react with steam to form the metal oxide and hydrogen.

Answer: (c)
Explanation:
Aqua regia, (Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few re-agents that is able to dissolve gold and platinum.

Answer: (c)
Explanation:
The following general properties for ionic compounds-
(i) Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.
(ii) Melting and Boiling points: Ionic compounds have high melting and boiling points (see Table 3.4). This is because a considerable amount of energy is required to break the strong inter-ionic attraction.
(iii) Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
(iv) Conduction of Electricity: The conduction of electricity through a solution involves the movement of charged particles.

Answer: (b)

Answer: (c)
Explanation:
Melting points and boiling points of some compounds of carbon :
Compound Melting point (K) Boiling point (K)
Acetic acid (CH3 COOH) 290 391
Chloroform (CHC13) 209 334
Ethanolji(CH3CH20H) 156 351
Methane (CH4) 90 111

Answer: (c)
Explanation:
Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings. Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent element. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements giving rise to compounds with specific properties which depend on the elements other than carbon present in the molecule.

Answer: (b)
Explanation:
The element carbon occurs in different forms in nature with widely varying physical properties. Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid threedimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. Fullerenes form another class of carbon allot- ropes. The first one to be identified was C-60 which has carbon atoms arranged in the shape of a football.

Answer: (a)
Explanation:
The valencies of all the atoms are satisfied by single bonds between them. Such carbon compounds are called saturated compounds. These compounds are normally not very reactive.

Answer: (a)
Explanation:
A homologous series is a series of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched. As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation. But the chemical properties, which are determined solely by the functional group, remain similar in a homologous series.

Answer: (b)
Explanation:
Alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids, that is, adding oxygen to the starting material. Hence, they are known as oxidising agents. Addition reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains. The concentrated sulphuric acid can be regarded as a dehydrating agent which removes water from ethanol.

Answer: (a)
Explanation:
Ethanol is an important industrial solvent. To prevent the misuse of ethanol produced for industrial use, it is made unfit for drinking by add ing poisonous substances like methanol to it. Dyes are also added to colour the alcohol blue so that it can be identified easily. This is called denatured alcohol. Sugarcane juice can be used to prepare molasses which is fermented to give al-cohol (ethanol). Some countries now use alco hoi as an additive in petrol since it is a cleaner fuel which gives rise to only carbon dioxide and water on burning in sufficient air (oxygen).

Answer: (b)
Explanation:
In the year 1817, Johann Wolfgang Dobereiner, a German chemist, tried to arrange the elements with similar properties into groups. He identi- fled some groups having three elements each. So he called these groups triads’. Dobereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

Answer: (d)
Explanation:
In 1866, John Newlands, an English scientist, arranged the then known elements in the order of increasing atomic masses. He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element. He found that every eighth element had properties similar to that of the first. He compared this to the octaves found in music. It was found that the Law of Octaves was applicable only upto calcium, as after calcium every eighth element did not possess properties similar to that of the first. It was assumed by Newlands that only 56 elements existed in nature and no more elements would be discovered in the future.

Answer: (d)
Explanation:
Dobereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. In 1866, John Newlands, an English scientist, arranged the then known elements in the order of increasing atomic masses. He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element. When Mendeleev started his work, 63 elements were known. He examined the relationship between the atomic masses of the elements and their physical and chemical properties. Mendeleev’s Periodic Law was modified and atomic number was adopted as the basis of Modem Periodic Table and the Modem Periodic Law can be stated as follows: ‘Properties of elements are a periodic function of their atomic number.

Answer: (c)
Explanation:
The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom. As the atomic number increases from left to right in a period, therefore valence electrons also increases. The atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the.size of the atom. Therefore, it becomes difficult to lose electrons. Hence, metallic character decreases across a pe-riod. Non-metals are found on the right-hand side of the Periodic Table towards the top. These trends also help us to predict the nature of oxides formed by the elements because it is known to you that the oxides of metals are basic and that of nonmetals are acidic in general.