Science Ncert Exemplar 2019 Solutions for Class 8 Science Chapter 18 - Pollution Of Air And Water

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The gas that is 21% part of the air and essential for the survival of human beings is oxygen.

Hence, the correct answer is option (b).

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Windmill is not a source of air pollution. It is regarded as an alternative source of energy which uses sped of winds to generate energy.

Hence, the correct answer is option (c).

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Boojho should use a school bus to reduce air pollution.

Hence, the correct answer is option (b).

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Reduce, reuse and recycle is the mantra to save water conciously at the individual level.Replace is not a way to conserve water. 

Hence, the correct answer is option (a).

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Air pollution is affecting Taj Mahal by corroding it and turning its white marble pale yellow.

Hence, the correct answer is option (a).

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Carbon monoxide is produced by the incomplete combustion of fuels like wood, coal, kerosene, petrol and diesel.

Hence, the correct answer is option (c).

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The phenomenon of marble cancer Is due to acid rain. Marble cancer is corrosion of buildings or monuments by acid rain.

​Hence, the correct answer is option (d).

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Water which is suitable for drinking is called potable water.

Hence, the correct answer is option C.

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Distillation removes nearly all the impurities like dissolved minerals, inorganic salts, heavy metals and bacteria from water.

Hence, the correct answer is option B.

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Swimming in the pond will produce least pollution of water because hazardous chemicals, gases and sewage are least likely to be mixed with water during this activity.

Hence, the correct answer is option D.

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Lakhs of trees are planted in July every year. This occasion is known as Van Mahotsav.

Hence, the correct answer is option C.

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Nitrogen gas is the major component of air at about 78% but it is not a greenhouse gas. Gases like carbon dioxide, methane, nitrous oxide and water vapour are greenhouse gases.

Hence, the correct answer is option A.

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Chlorofluorocarbons (CFCs) are used in refrigerators and air conditioners. They damage the ozone layer of the atmosphere.

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Two sources which cause air pollution due to suspended particulate matter are:

• Burning of diesel and petrol by automobiles
• Industrial processes like steel making and mining

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Sulphur dioxide and nitrogen dioxide gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid which makes the rain acidic.

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We can use this data to create awareness about air pollution among family, friends and neighbours.

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Solar energy and wind energy are the two alternative sources of energy which do not cause any pollution.

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Arsenic and lead are the two water pollutants which are toxic for plants and animals.

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No, it is not right to burn dry leaves because it leads to air pollution causing breathing problems. Alternatively, they should be put in a compost pit as they are biodegradable and will be converted into manure to be used for crops.

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At a busy traffic intersection, large number of vehicles stop for a short time and release high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke. Therefore, the level of air pollution is higher at a busy traffic intersection.

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(a) When air is contaminated by unwanted substances which have a harmful effect on both the living and non-living, it is referred to as air pollution.
(b) Many industries are responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.
(c) While brushing your teeth, leaving the tap running may waste several litres of water.
(d) Water which is suitable for drinking is called potable water.
(e) Water which looks clean still has disease carrying microorganisms and dissolved impurities.

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Column A                                         Column B
(a) sulphur dioxide                 (iii) acid rain
(b) carbon dioxide                 (iv) green house gas
(c) carbon monoxide             (ii) reduces oxygen carrying capacity of blood
(d) chlorofluorocarbons        (i) damage ozone layer

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The wrong statements are:
(a) We can survive for some time without air but we cannot survive even for a few minutes without food.
(c) Carbon monoxide is produced by complete burning of fuels such as coal, petrol, diesel.
(e) Water which is suitable for drinking is called soft water.

The corrected from of wrong statements are:
(a) We can survive for some time without food but we cannot survive even for a few minutes without air.
(c) Carbon monoxide is produced by incomplete burning of fuels such as coal, petrol, diesel.
(e) Water which is suitable for drinking is called potable water.

Answer:

(a) Air contains 78% nitrogen and 21% oxygen.
(b) Vehicles produce high level of pollutants like carbon dioxide, nitrogen oxides, carbon monoxide and smoke.
(c) Carbon dioxide, methane, nitrous oxide and water vapour are known as greenhouse gases.
(d) Gangotri glacier in Himalaya has started melting because of global warming.
(e) Whenever harmful substances such as sewage, toxic chemicals, silt, etc. get mixed with water, the water becomes polluted.

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The full form of CFCs is chlorofluorocarbons. They are used in refrigerators, air conditioners and aerosol sprays. They are considered as pollutants because they damage the ozone layer of the atmosphere.

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The industries located in the Taj Mahal Zone in Agra such as automobiles, rubber processing, chemicals and the Mathura oil refinery, have been releasing sulphur dioxide and nitrogen dioxide gases which react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These acids come down with rain and result in acid rain which corrodes the marble of the Taj Mahal. Also, the soot particles emitted by Mathura oil refinery has contributed towards the yellowing of the marble. Therefore, it is advised that industries should switch over to cleaner fuels such as CNG and LPG in the Taj Mahal Zone in Agra.

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A part of the solar radiation that falls on the earth is absorbed by the earth’s surface and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere that further warms the earth. This phenomenon is called the greenhouse effect. Carbon dioxide (CO₂) is one of the major greenhouse gases in the atmosphere. It is necessary for the existence of life on earth but an excess of CO₂ in the atmosphere poses serious consequences. Plants maintain a balance by utilising CO₂ from the atmosphere for photosynthesis. But widespread deforestation has led to an increase in the amount of CO₂ in the air as the number of trees which consume CO₂ have been reduced. On the other hand, human activities have been continuously releasing lot of CO₂, thus, contributing to the accumulation of CO₂ in the atmosphere. As a result, the average temperature of the earth’s atmosphere is gradually increasing which is called global warming. Hence, it is said that CO₂ contributes to global warming.

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Widespread deforestation has led to an increase in the amount of CO₂ in the air as the number of trees which consume CO₂ have been reduced. On the other hand, human activities have been continuously releasing lot of CO₂, thus, contributing to the accumulation of CO₂ in the atmosphere. As a result, the average temperature of the earth’s atmosphere is gradually increasing which is called global warming. Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals. Therefore, we should plant trees and nurture the ones already present in the neighbourhood to reduce air pollution and global warming.

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The traditional way of purifying water to make it fit for drinking is as follows:

• A plastic bottle is taken and cut it into two halves at the centre.
• The upper half is used as a funnel by putting it upside down in the lower half.
• Then, filter layers are made in it with paper napkin or a fine cloth followed by, cotton, sand and then gravel.
• Now dirty water is poured through the filter and the water obtained is filtered water.
• Further, the filtered water may be boiled to kill the germs present in the water.

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We can save water by the following ways:

• Reduce- We should close the tap while brushing our teeth.
• Reuse- We should reuse the water used for washing vegetables to water plants in the garden.
• Recycle- We should recycle the dirty water by adding chlorine tablets or bleaching powder to the water

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(i) The various sources of water pollution can be classified as point sources and non-point sources.

(ii) Point sources of water pollution are the easily identified sources of pollution such as municipal and industrial discharge pipes, where pollutants enter the water source.

(iii) Two non-point sources of water pollution are agricultural run off and acid rain.

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