Pollution of Air and Water Class 8 CBSE NCERT Notes

Science Class 8th Notes of Chapter 18 – Pollution Of Air And Water

Q 1: What is pollution?

A 1: The presence of unusually high concentrations of harmful or poisonous substances in the environment (air, water, etc.) is called pollution.

Q 2: What is a pollutant?

A 2: An unwanted and harmful substance that contaminates the environment such as air and water is called a pollutant.

Q 3: What is air?

A 3: Air is a mixture of gases present all around us. The two main gases present in air are nitrogen and oxygen.

Nitrogen makes up about 78% of air whereas oxygen makes up to about 21% of air by volume. Air also contains small amounts of carbon dioxide, argon and water vapour.

The mixture of gases containing nitrogen, oxygen, carbon dioxide, argon and water vapour gives us pure air or clean air which is good for us.

Q 4: What is there in polluted air?

A 4: Polluted air may contain harmful substances such as carbon monoxide, sulphur dioxide, nitrogen oxides, smoke and dust etc.

Q 5: What is air pollution?

A 5: The contamination of air with harmful gases like sulphur dioxide, nitrogen oxides, carbon monoxide, smoke and dust etc. is called air pollution.

Q 6: What is air pollutant?

A 6: The substance whose presence in air make it impure or contaminated is called an air pollutant.

A substance becomes an air pollutant when it is present in air in such concentration which is high enough to have a harmful effect on the living and non living things.

Q 7: What are major air pollutants?

A 7: The major pollutants which cause air pollution are: Sulphur dioxide, Nitrogen oxides, Carbon monoxide, excess of carbon dioxide, Chlorofluorocarbons and Suspended particulate matter (such as Dust, Smoke and Fly ash).

Q 8: What are the sources of air pollution?

A 8: Most of the air pollution is caused by the burning of fuels such as wood, cow dung cakes, kerosene, petrol and diesel in homes, motor vehicles (automobiles), factories and thermal power plants, etc.

The various sources of air pollution are given below:

i). Smoke emitted from homes by the burning of fuels like wood, cow-dung cakes, kerosene and coal.

ii). Exhaust gases emitted by motor vehicles (automobiles) due to burning of petrol and diesel causes air pollution. Motor vehicles are the major cause of air pollution in big cities.

iii). Smoke emitted by factories and thermal power plants due to burning of coal.

iv). Oil refineries and industries engaged in the production of metals and manufacture of chemicals.

v). Stone crushers, cement factories, asbestos factories and lead processing units cause air pollution.

vi). Use of chlorofluorocarbons (CFC) in refrigeration, air conditioning and aerosol sprays causes air pollution.

vii). Smoking.

All the above sources of air pollution are man-made sources of air pollution in which pollutants are added to air by various human activities.

Forest fires and volcanic eruptions are the two natural sources of air pollution which put up smoke and dust into the air.

Q 9: What are names, sources and harmful effects of air pollutants?

A 9: Following are the names, sources and harmful effects of various air pollutants:

i). Sulphur Dioxide

Sulphur dioxide is produced by burning of coal in factories and thermal power plants. It is also produced by the burning of petrol and diesel in motor vehicles. Oil refineries and burning of coal also produces sulphur dioxide in air.

Sulphur dioxide (SO2) gas is the polluted air causes respiratory problems. It may even cause permanent lung damage. Sulphur dioxide gas in polluted air produces acid rain.

Sulphur dioxide also contributes to the formation of a deadly air pollutant called smog.

ii). Nitrogen Oxides

Nitrogen oxides are produced by the burning of fuels like petrol and diesel in motor vehicles. They are also produced by the burning of coal in factories and thermal power plants. Oil refineries also produce and emit nitrogen oxides into the air.

Nitrogen oxides attack breathing system and lead to lung congestion. They also attack skin. Nitrogen oxides present in polluted air produce acid rain. Nitrogen oxides also contribute to the formation of smog. Smog is deadly air pollutant which is formed by the combination of smoke and fog (the minute water particles suspended in air near the surface of earth during cold weather in winter). The carbon particles, nitrogen oxides and sulphur dioxide etc. of smoke combine with the condensed water vapour called fog to form smog. Smog causes cough and aggravates (makes worse) asthma and other lung diseases, especially in children.

iii). Carbon Monoxide

Carbon monoxide (CO) is produced by the incomplete combustion of fuels like wood, coal, kerosene, petrol and diesel in homes, factories and motor vehicles. The exhaust gases of motor vehicles contain carbon monoxide which they emit into air. Cigarette smoke also contains carbon monoxide.

Carbon monoxide is a very poisonous gas. When inhaled, carbon monoxide combines with the haemoglobin of our blood and reduces the oxygen carrying capacity of blood. This lack of oxygen causes respiratory problems and causes suffocation. If too much carbon monoxide is inhaled, it may even cause death.

iv). Carbon Dioxide

Carbon dioxide (CO2) is produced in excessive amounts by the burning of large quantities of fuels such as wood, coal, kerosene, petrol, diesel, LPG and CNG is homes, factories and motor vehicles.

Carbon dioxide is the main greenhouse gas which traps sun’s heat in the earth’s atmosphere by producing greenhouse effect which leads to global warming.

v). Chloro-Fluoro-Carbons (CFCs)

Chlorofluorocarbons are the chemical compounds made of chlorine, fluorine and carbon elements. They are commonly known as CFCs.

Chlorofluorocarbons are used in refrigeration, air conditioning and aerosol sprays. Chlorofluorocarbons are industrially useful gases but they also behave are air pollutants because of their damaging effect on ozone layer.

Chlorofluorocarbons are depleting the useful ozone layer of the upper atmosphere. They reach the upper layer and react with the ozone gas of ozone layer and destroy it gradually.

Ozone layer prevents the harmful ultraviolet radiations of the sun from reaching the earth.

The destruction of ozone layer by CFCs will allow the extremely harmful ultraviolet radiations of the sun to reach the earth. These ultraviolet radiations can cause skin cancer, cataract, and destruction of plants, including crops.

vi). Suspended Particulate Matter (SPM)

The finely divided solid or liquid particles suspended in air are called suspended particulate matter. Some of the examples of suspended particulate matter are: Dust Smoke and Fly ash.

a). Dust consists of tiny particles of earth.

Dust is produced by blowing wind, heavily traffic on roads, stone crushers and construction activities. Dust in air spoils our clothes and reduces visibility. Dust produces allergic reaction in human body and aggravates diseases like bronchitis. Dust covers the leaves of plants and trees and prevents photosynthesis.

b). Smoke is mainly tiny particles of carbon in air. Smoke is produced by the burning of fuels like wood, cow-dung cakes, coal, kerosene, petrol, and diesel in homes, factories, thermal power plants and motor vehicles. Smoke present in air spoils our clothes and blackens the buildings. Smoke attacks our lungs and causes respiratory diseases.

c). The minute ash particles formed by the burning of coal and carried into air by the gases produced during burning, is called fly ash.

Fly ash is emitted by the chimneys of coal based thermal power plants.

Fly ash particles present in air cause irritation to the eyes, skin, nose, throat and respiratory tract. Continued breathing in air containing fly ash causes diseases like bronchitis and lung cancer.

Q 10: What are the two extremely harmful effects of air pollution on the environment?

A 10: The two extremely harmful effects on the environment are acid rain and greenhouse effect.

Q 11: What is acid rain?

A 11: Acid rain is that rain which contains small amounts of acids formed from acidic gases like sulphur dioxide and nitrogen oxides present in polluted air. Acid rain contains very small solutions of sulphuric acid and nitric acid.

It happens as follows: The burning of fossil fuels like coal and oil in factories, thermal power plants and oil refineries, and petrol and diesel in motor vehicles produce acidic gases like sulphur dioxide and nitrogen oxides which go into air and pollute it. Sulphur dioxide reacts with water vapour present in the atmosphere to form sulphuric acid whereas nitrogen oxides react with water vapour present in the atmosphere to form nitric acid. These acids dissolve in rainwater and fall to the earth in the form of acid rain.

Q 12: What are the damages caused by acid rain?

A 12: The damages caused by acid rain are very, very slow and hence cannot be seen immediately. Acid rain has the following harmful effects:

i). Acid Rain Destroys Forests And Crops

Acid rain damages the forest trees by destroying their leaves. It causes the leaves of trees to turn yellow and fall off. In the absence of leaves, the roots of trees cannot absorb water from the soil. And due to lack of water the trees die.

Acid rain also damages a lot of crop plants very year and causes a big loss to the farmers. Acid rain makes the soil acidic. This acidic soil is not good for the growth of crop plants.

ii). Acid Rain Kills Aquatic Animals Such as Fish

Acid rain causes the water in ponds, lakes and rivers to become much more acidic and unsuitable for the survival of aquatic animals and plants. Due to high acidity of water, the aquatic animals such as fish get killed.

iii). Acid Rain Corrodes the Statues, Buildings And Historical Monuments and Damages Them Slowly

The statues, buildings and monuments are made of marble and limestone etc. The acids present in acid rain react with the carbonates present in marble and limestone of a statue, building or monument and corrode it slowly (dissolve slowly). In this way, acid rain makes the statues, buildings and monuments to crumble away slowly.

Q 13: How is Taj Mahal getting affected due to air pollution?

A 13: The Taj Mahal at Agra is a beautiful historical monument made of pure, white marble.

The air pollution around Taj is discolouring its white marble and also corroding it slowly. This poses a threat to the beauty of Taj Mahal.

The Mathura Oil Refinery near Agra as well as various industries in and around Agra are emitting gaseous pollutants such as sulphur dioxide and nitrogen oxides into the air which cause acid rain. The acids present in acid rain react with marble (calcium carbonate) of Taj Mahal monument and corrode it slowly.

The slow corrosion or eating up of marble of a monument by acid rain is known as “Marble Cancer”.

The suspended matter such as soot (carbon formed by incomplete combustion) particles emitted in the smoke from Mathura Oil Refinery is discolouring the pure white marble of Taj Mahal by turning it yellowish.

Q 14: What are steps taken by Indian government to protect Taj?

A 14:  The Supreme Court Of India has taken several steps to save Taj Mahal from the damage being caused by air pollution (acid rain etc.). It has ordered all the industries in Agra area to switch over to cleaner fuels like CNG and LPG to reduce air pollution. It has also asked vehicles to be run on CNG or unleaded petrol in the Taj Mahal area.

Q 15: What is greenhouse?

A 15: The greenhouse is a structure or building made of glass walls and glass roof in which the plants that need protection from cold weather are grown.

The glass walls and glass roof of a greenhouse allows the sun’s heat rays to go in freely but do not allow the inside heat (reflected by soil, plants and other things in the greenhouse) to go out. In this way, more and more of sun’s heat rays are trapped inside the greenhouse due to which the temperature in the greenhouse rises. 

So, even without an internal supply of heat, the temperature inside a greenhouse becomes higher than that outside.

This heat is beneficial for the growth of plants inside the greenhouse (when the outside temperature is very low during winter season). The glass walls and glass roof acts as a heat trap for sun’s heat rays.

Q 16: What is greenhouse effect in Earth’s atmosphere?

A 16: Due to the presence of a carbon dioxide layer around the earth, our atmosphere acts like the glass roof of an ordinary greenhouse and allows sun’s heat rays to be trapped within the earth’s atmosphere. This is called greenhouse effect.

The sun is an extremely hot object due to which the heat rays emitted by the sun are of shorter wavelengths. 

The shorter wavelength heat rays coming from the sun can pass through the glass walls and glass roof of a greenhouse and go inside it. On the other hand, the inside objects of glasshouse are much less hot (than the sun), so they emit heat rays of longer wavelengths. The longer wavelength heat rays emitted by the inside objects of the greenhouse cannot pass through the glass walls and glass roof of a greenhouse and go out. 

Thus glass is a material which allows sun’s heat rays to come in but does not allow heat rays to go out. This is called greenhouse effect.

Q 17: What are the uses of greenhouse effect in earth atmosphere?

A 17: The warming up or heating up of the earth’s atmosphere due to the trapping of sun’s heat rays by carbon dioxide in the atmosphere is called greenhouse effect.

The warming or heating of the earth produced by greenhouse effect is important for the existence of life on earth. This is because it is due to the warming of earth by the greenhouse effect that the earth has become a habitable planet having millions of different life forms in it. If there were no warming up of the earth’s atmosphere due to the greenhouse effect produced by carbon dioxide gas in the atmosphere, the whole earth would have been converted into an extremely cold planet, making the existence of life difficult on it.

Q 18: What is causing increased greenhouse effect in earth’s atmosphere?

A 18: Too much of carbon dioxide in the earth’s atmosphere is causing excessive heating of earth’s atmosphere and increased greenhouse effect.

Q 19: Why is the amount of CO2 in earth’s atmosphere increasing?

A 19: Following are the reasons contributing to the increase in the amount of CO2 in earth’s atmosphere:

i). Rapid burning of fossil fuels (coal, petrol and diesel) to meet the energy requirements of increasing population.

ii). Deforestation and acid rain which is decreasing the count of plants and trees due to which less amount of CO2 is getting converted to oxygen.

Q 20: Explain global warming.

A 20: The undue rise in the temperature of earth’s atmosphere due to excessive greenhouse effect produced by increasing amounts of carbon dioxide gas in the atmosphere is called global warming.

Q 21: How is global warming harmful to us?

A 21: Global warming is harmful to us in the following ways:

i). Global Warming Can Cause Sea-Levels to Rise Dramatically

This rise in temperature of atmosphere due to excessive greenhouse effect or global warming will melt the enormous amount of ice lying on the poles of the earth. The huge amount of water produced by the melting of polar ice will raise the level of water in the seas and oceans, and flood the low-lying areas of the earth. This will cause damage to life and property.

ii). Global Warming Can Reduce Rainfall in Some Area of the Earth Leading to Droughts (excessive shortage of water).

Increased temperatures cause more evaporation, which causes clouds to form faster and rain faster. This means some places will receive greater amount of rain (and potentially floods) and other places will receive less rain (and potentially droughts).

An increase in the earth’s atmospheric temperature by even as little as 0.5 degree Celsius can have serious consequences for all.

Q 22: What is Kyoto Protocol?

A 22: Kyoto protocol was an agreement signed by many countries at Kyoto, Japan in December, 1997 to minimise the burning of fossil fuels and thus reducing the greenhouse effect in earth’s atmosphere.

Q 23: What are greenhouse gases? Name them.

A 23: Those gases which can trap sun’s heat rays in the earth’s atmosphere by producing greenhouse effect leading up to the heating of earth’s atmosphere are called greenhouse gases.

Water vapour (H20 (g)), Carbon dioxide (CO2), Methane (CH4), Nitrous Oxide (N2O) and Ozone (O3) are the main greenhouse gases.

Q 24: Which is the main greenhouse gas?

A 24: Carbon dioxide (CO2) is the main greenhouse gas.

Q 25: What is global warming?

A 25: The undue rise in the temperature of earth’s temperature due to excessive greenhouse effect produced by increasing amounts of carbon dioxide gas in the atmosphere is called global warming.

Q 26: Do nitrogen and oxygen play any role in the greenhouse effect of the nature?

A 26: The main constituents of the atmosphere, nitrogen and oxygen, are not greenhouse gases. They do not play any role in the greenhouse effect in nature.

Q 27: How can air pollution be controlled?

A 27: The polluted air is damaging our health and property gradually. So, air pollution must be controlled as soon as possible.

Some of the ways of controlling air pollution are given below:

i). By using smokeless fuels

The air pollution can be controlled by using smokeless fuels like LPG, PNG (Piped Natural Gas) and Bio-gas for cooking food (instead of wood, cow-dung cakes, or coal). Solar cookers can also be used for cooking food. Solar water heaters should be installed for obtaining hot water.

ii). The air pollution from motor vehicles can be reduced by suing CNG (Compressed Natural Gas) as fuel in place of petrol and diesel. CNG is a very clean fuel which does not pollute air.

iii). Unleaded petrol should be used. Unleaded petrol does not have lead, a dangerous air pollutant that affects brain of children.

iv). Washing air pollution of factories etc. with jets of water

The air pollution from factories, thermal power plants, oil refineries and chemical industries can be controlled by washing down their smoke and waste gases with jets of water. When the smoke and waste gases are sprayed by jets of water before they reach chimney, then soot present in smoke is washed away and most of the poisonous gases like sulphur dioxide and nitrogen oxides get dissolved in water.

v). Using non-polluting energy sources

The air pollution can be controlled by using non-polluting sources of energy like solar energy, wind energy and hydro energy for generating electricity. This will reduce the use of fossil fuel like coal which is used for generating electricity at thermal power plants and causes air pollution.

Q 28: What role can we play in controlling air pollution?

A 28: We can also contribute in the efforts to control air pollution and improve the quality of air around us in the following ways:

i). We should not burn dry leaves, papers and garbage in the open. Leaves should be converted into compost (natural fertiliser) by burying in a pit; used papers should be sent to paper mills for recycling; and garbage should be deposited in the garbage dumps established by the Municipal Corporation of the city.

ii). We should save electricity.

If all of us start saving electricity by avoiding its wastage in homes, schools, shops, offices and factories, the demand for electricity will decrease. This will lead to the burning of less coal to generate electricity at coal thermal power stations. And burning of less coal will reduce air pollution.

iii). We should grow more trees and also take care of the existing trees in our neighbourhood. Trees reduce pollution by absorbing excess carbon dioxide from the air. All of us should participate in Van Mahotsav functions when lakhs of trees are planted in July every year.

iv). We should join “Say No to Crackers” campaign organised by children of many schools during Diwali days to reduce the level of air pollution during the festival season.

v). We should use bicycle for covering short distances. This will save precious fuel like petrol and also reduce air pollution.

vi). If the school is not far off, we should go to school on foot or by a bicycle. Otherwise, we should use the school bus or public transport bus for going to school.

In no case should we use a car individually to go to school. If, however, sufficient number of students goes to the same school from an area, then a car pool can be formed for going to school.

Q 29: What is water pollution?

A 29: The contamination of water of rivers, lakes and ponds, etc. with unwanted and harmful substances is called water pollution. Water is said to be polluted when it becomes unfit for drinking or bathing.

Q 30: What are water pollutants?

A 30: The unwanted and harmful substances which make the water impure or contaminated are called water pollutants.

The major pollutants which cause water pollution are: Sewage, Fertilisers, Pesticides and Industrial wastes.

Hot water from power plants and industries is also considered a pollutant. This is because the hot water raises the temperature of the river water or lake water. The rise in the temperature of river water or lake water has an adverse effect on the animals and plants living in it.

Q 31: What are the major sources of water pollution? Explain them.

A 31: The major sources of water pollution are:

i). Dumping of untreated sewage into rivers causes water pollution.

The waste water containing human excreta and carried in sewers (underground pipes) is called sewage. At many places, untreated sewage from homes is dumped into rivers which pollute the river water. Sewage contains several harmful miro-organisms such as bacteria, protozoa, fungi, viruses and parasites (worms etc.) which cause serious diseases in humans.

The drinking of river water contaminated with sewage can cause water borne diseases such as cholera, typhoid, diarrhoea, dysentery and jaundice.

ii). Use of Excessive Fertilisers In Agriculture Causes Water Pollution.

The water pollution caused by fertilisers used in agriculture decreases the amount of dissolved oxygen in water bodies and leads to death of fish and other aquatic animals.

iii). Use Of pesticides In Agriculture Causes Water Pollution.

The farmers use toxic chemicals (poisonous chemicals) called pesticides in standing crops in the fields to protect them from pests and diseases. Some of these pesticides dissolve in rain water and run into rivers, lakes and ponds and pollute their water. These poisonous pesticides kill the aquatic animals like fish. The non-biodegradable pesticides in the polluted water are absorbed by aquatic plants. These aquatic plants are then eaten by aquatic animals like fish. During this, pesticides are transferred from aquatic plants to fish. And when a person eats the fish grown in polluted water, the pesticides present in fish enter his body and damage his health.

iv). Discharging of untreated industrial wasted into rivers and lakes causes water pollution.

The toxic chemicals present in industrial wastes are the compounds of harmful metals such as mercury, lead arsenic, nickel and cadmium. These toxic industrial wastes are released by chemical industry, textile industry, leather industry, paper mills, sugar mills, oil refineries, dyes and paint manufacturing industries.

The water of rivers and lakes polluted with toxic industrial wastes can kill fish and other aquatic animals which live in this river or lake.

The toxic metal compounds present in this polluted water can enter the human body through the food chain (like eating fish grown in this polluted water). They can damage our nervous system and cause diseases such as blood poisoning and cancer.

Q 32: How has the water of river Ganga getting polluted?

A 32: The water of river Ganga has been highly polluted because the villages, towns and cities which are situated on the banks of this very long river throw large quantities of garbage, untreated sewage, toxic industrial wastes, dead bodies of infants and many other harmful things into the river.

People immerse idols of gods and goddesses in the river water.

They also throw ashes of dead persons, flowers and polythene bags into the river.

People can be seen bathing and washing dirty clothes and utensils in the river water.

They also bathe their cattle like cows and buffaloes in the river.

Some people even defecate near the river water.

Q 33: What is Ganga Action Plan (GAP)?

A 33: Ganga Action Plan was an ambitious plan launched in 1985 to reduce the pollution level in the water of river Ganga.

Q 34: What should be done to control water pollution?

A 34: The various ways of controlling or minimising water pollution are as follows:

i). Sewage should be treated properly at sewage treatment plants to make it harmless before discharging it into nearby rivers.

ii). Farmers should use correct amounts of fertilisers and pesticides in the field so that excessive amounts of these harmful agricultural chemicals are not washed into rivers, lakes or ponds.

iii). All the industries should treat the toxic wastes produced by them suitably to make them harmless before discharging them into rivers.

iv). Water pollution prohibition laws which exist for the industries producing toxic chemical wastes should be implemented strictly by the concerned authorities.

v). Garbage (household waste) should not be thrown into open drains, rivers, lakes or ponds. Dead bodies should not be thrown into rivers. Dead bodies should be cremated or buried properly to prevent pollution of water.

vi). People should be made aware of the harmful effects of water pollution so that they may co-operate and help in preventing it.

Q 35: How can water be conserved?

A 35: The treatment of polluted water from livers and lakes costs a lot of money. We should conserve or save water by using it carefully, economically and avoiding its wastage because there is scarcity or shortage of fresh water in our country. The various ways to conserve water at home are as follows:

i). Turn off tap immediately after use. Get the leaking taps repaired immediately. A leaking tap that drips once every second wastes a few thousand litres of water every year.

ii). Brush your teeth by filling water in a mug. Leaving the tap running while brushing the teeth may waste several litres of water. Take bath by filling water in a bucket and not directly under the running tap.

iii). Wash the utensils by filling water in a basin and not under the running tap.

iv). Use water from washing rice, pulses, vegetables and fruits for watering the plants at home.

v). Do not use the full flush from the cistern in the toilet when a half flush is sufficient.

Q 36: What is potable water?

A 36: The term potable means drinkable. The water which is safe for drinking is called potable water.

The tap water which we get through pipes in our home is clean and usually without any smell (or odour). It is said to be safe for drinking.

Q 37: Does the water that looks clean and without any foul smell always safe for drinking?

A 37: No, the water which looks clean and has no foul smell is not always safe for drinking.

The water may have some disease causing micro-organisms in it.

Q 38: What are some of the methods to make water safe for drinking?

A 38: Some of the methods to make water safe for drinking are:

i). By Filtering (by using porcelain candle filter or electric water filter)

In candle type water filter, the tap water is filled in a container having candles made of porcelain fixed in it. This water gets filtered thoroughly on passing through the tiny pores of porcelain candles and drops into another container kept below. The water which collects in the lower container is very safe for drinking.

ii). By Boiling

When water is heated, it boils at a temperature of 100 degree Celsius. At this high temperature, all the harmful micro-organisms or germs present in water are killed and it becomes absolutely safe for drinking. Many households use boiling as a method for obtaining safe drinking water.

iii). By Chlorination (by adding chlorine tablets)

Chlorination is done by adding chlorine tablets to water. Chlorine kills all the harmful micro-organisms or germs present in water and make it absolutely safe for drinking. We should not use more chlorine tablets than specified. Bleaching powder can also be used for chlorination of water and making it safe for drinking.

Q 39: How can you make a “simple water filter” by using the commonly available materials around us?

A 39: We can make a “simple water filter” from commonly available materials around us as follows:

Take a plastic bottle and cut it into two halves keeping the upper part somewhat smaller than the lower part as the lower part will have clean water in it.

Turn the upper half of plastic bottle upside down and place it in the lower half of plastic bottle so that it may work like a funnel.

Make layers in the upper part of water bottle with a piece of fine cloth, followed by cotton, sand and then gravel (stone with size in between 2 mm and 4 mm).

Now pour dirty water from the top end of filter.

We will see that clear water collects in the lower half of plastic bottle slowly. The suspended impurities of dirty water have been removed by filtration through the water filter.

Q 40: What is ozone hole?

A 40: Over the south pole of earth, a big hole has been made in the ozone layer due to the destruction of ozone gas by CFCs. This hole is called the ozone hole.