Pollution of Air and Water Class 8 Science Chapter 18 Extra Questions with Answers are provided here. We prepared these extra questions based on the latest NCERT Class 8 Science Book. CBSE Class 8 Science Chapter 18 Pollution of Air and Water Extra Questions will help you to properly understand a particular concept of the chapter.

Very Short Answer Type Question

Question 1: Which air pollutant reduces the oxygen-carrying capacity of the blood?

Answer: Carbon monoxide reduces the oxygen-carrying capacity of the blood.

Question 2: What protects us from harmful ultraviolet rays of the sun?

Answer: The ozone layer protects us from harmful ultraviolet rays of the sun.

Question 3: Name three greenhouse gases present in the atmosphere.

Answer: methane, nitrous oxide and carbon dioxide

Question 4: What is potable water?

Answer: Water which is purified and fit for drinking is known as potable water.

Question 5: Which gas contributes maximum to greenhouse effect?

Answer: Carbon dioxide gas contributes maximum to greenhouse effect.

Question 6: Name one gas which damages the ozone layer of the atmosphere.

Answer: Chlorofluorocarbons (CFCs) damage the ozone layer of the atmosphere.

Question 7: Why is Ozone layer important?

Answer: Ozone layer protects us from harmful ultraviolet rays of the sun.

Question 8: Name some toxic metals whose compounds are present in industrial wastes.

Answer: arsenic, lead and fluorides

Question 9: Name any two types of chemicals used in agriculture which cause water pollution.

Answer: pesticides and weedicides

Question 10: Name any three diseases caused by drinking polluted water containing sewage.

Answer: cholera, typhoid and jaundice

Question 11: Which gas is mainly responsible for greenhouse effect?

Answer: Carbon dioxide is the gas which is mainly responsible for greenhouse effect.

Question 12:  What are the main gases that cause acid rain?

Answer: Sulphur dioxide and nitrogen dioxide are the main gases that cause acid rain.

Question 13: Where are chlorofluorocarbons used?

Answer: Chlorofluorocarbons (CFCs) are used in refrigerators, air conditioners and aerosol sprays.

Question 14:  What are the major pollutants of air?

Answer: Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air.

Question 15: What air pollutants are released by motor vehicles?

Answer: Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke.

Short Answer Type Questions

Question 1: What is air pollution?

Answer: Air pollution is the contamination of air by impurities which may have a harmful impact on the living organisms and the non-living components.

Question 2: Write one source and one harmful effect of carbon monoxide.

Answer: Carbon monoxide is produced from incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood.

Question 3: Write one source and one harmful effect of sulphur dioxide.

Answer: Sulphur dioxide is produced by combustion of fuels like coal in power plants. It can cause respiratory problems, including permanent lung damage.

Question 4: What is Kyoto Protocol?

Answer: The Kyoto Protocol is an international agreement that aimed to reduce carbon dioxide (CO2) emissions and the presence of greenhouse gases in the atmosphere.

Question 5: What is water pollution? Name any four major water pollutants.

Answer: Water pollution is the contamination of water by substances harmful to life. Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.

Question 6: What is global warming?

Answer: Accumulation of CO₂ in the atmosphere traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Question 7: How do pesticides cause water pollution?

Answer: Pesticides are sprayed on crop plants. These chemicals dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute ground water.

Question 8: Write one source and one harmful effect of oxides of nitrogen.

Answer: Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children.

Question 9: Why hot water released by power plants and industries is considered a pollutant?

Answer: Hot water released by power plants and industries is considered a pollutant because it raises the temperature of the water body and adversely affect the animals and plants living in it.

Question 10: Clear, transparent water is always fit for drinking. Comment

Answer: No, clear and transparent water is not always fit for drinking. Water which looks clean may still have disease carrying microorganisms and dissolved impurities. So, it is essential to purify water before drinking, for example, by boiling.

Long Answer Type Questions

Question 1: How do industries cause water pollution?

Answer: Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water. Examples are oil refineries, paper factories, textile and sugar mills and chemical factories. These industries cause chemical contamination of water. The chemicals released include arsenic, lead and fluorides which lead to toxicity in plants  and animals.

Question 2: Explain the differences between pure air and polluted air.

Answer: Pure air consists of a mixture of gases. By volume, about 78% of this mixture is nitrogen and about 21% is oxygen. Carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities.When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as polluted air.

Question 3: What is smog? How is it formed? What are its harmful effects?

Answer: A thick fog-like layer in the atmosphere, especially during winters made up of smoke and fog is called smog. Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children.

Question 4: Write any three ways of controlling water pollution.

Answer: Ways of controlling water pollution

• Sewage water should be treated to make it harmless before discharging it into water bodies such as lakes, rivers, and oceans.
• All the industries should treat the toxic wastes before discharging them into water bodies.
• Garbage should not be thrown into open drains, rivers, lakes or ponds.

Question 5: Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer: Excessive quantities of chemicals (fertilizers, pesticides and weedicides) which get washed from the fields act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in the water body gets used up. This results in a decrease in the oxygen level which may kill aquatic organisms.

Question 6: Describe the ‘Green House Effect’ in your own words.

Answer: The greenhouse effect is a warming of Earth’s surface and the air above it. The sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The trapped radiations further warm the earth. This process is called the greenhouse effect. Without this process, life would not have been possible on the earth.

Question 7: Describe the threat to the beauty of the Taj Mahal.

Answer:. The beauty of the Taj Mahal in white marble is being threatened by air pollution in the area surrounding the Taj. Due to increase in pollutants like sulphur dioxide and nitrogen dioxide in air, acid rain take place. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble.

Question 8: What are the different ways in which water gets contaminated?

Answer: Following are the different ways in which water gets contaminated:

• Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water.
• Pesticides and weedicides used for the protection of crops get dissolve in water and are washed into water bodies from the fields. They also seep into the ground to pollute ground water.
• Sometimes untreated sewage is thrown directly into rivers which pollute the river water.

Question 9: At an individual level, how can you help reduce air pollution?

Answer: An individual can reduce air pollution by:

• By using public transport or car pool as far as possible.
• By not using vehicles for short distances.
• By using clean fuels such as LPG and CNG instead of diesel and petrol.
• By disposing the garbage properly.
• By controlling the emissions from vehicles and household chimneys.
• By planting trees in the surroundings.
• By saying no to crackers.

Question 10: How water can be made safe for drinking?

Answer: Water can be made safe for drinking in the following ways:

• Filtration is one of the effective ways of purifying water. A popular household filter is a candle type filter.
• Water can be made safe for drinking by boiling. Boiling kills the germs present in the water.
• Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder to the water.

Question 11: How can we prevent wastage of water? (Any 4 points)

Answer: We can prevent wastage of water in the following ways:

• Reuse water for washing and for other household tasks. For example, water used for washing vegetables may be used to water plants in the garden.
• Turn off the tap immediately after use.
• Get the leaking taps repaired immediately.
• Brush teeth by filling water in a mug.

Question 12: What are the harmful effects of global warming?

Answer: Harmful effects of global warming are

• Global warming can cause sea levels to rise dramatically. In many places, coastal areas have already been flooded.
• Global warming could result in wide ranging effects on rainfall patterns, agriculture, forests, plants and animals.
• There has to be check on the emission of greenhouse gases at the present level. Otherwise, the temperature may rise by more than 2 degrees Celsius by the end of the century which is very dangerous.

Question 13:  Explain circumstances leading to acid rain. How does acid rain affect us?
Or
What is acid rain? How is acid rain caused? What are the harmful effects of acid rain?

Answer: Harmful gases such as sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain.

Effects of acid rain are:

• It corrodes the statues, buildings and historical monuments and damages them.
• It damages crops.
• It kills aquatic animals such as fish.

Question 14: You are a member of the municipal body of your town.

Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

Answer: To ensure the supply of clean water to all its residents the following steps must be taken:

• The main water source must be built in clean surrounding and should be maintained properly.
• Water should be treated properly to make it free from harmful germs, chemicals and impurities.
• Chemical methods such as chlorination must be used for purifying water.
• The area around water pipes must also be clean.

Question 15:  What is Ganga Action Plan? When was it launched? What was its purpose?

Answer: An ambitious plan to save the river, called the Ganga Action Plan was launched in 1985. It aimed to reduce the pollution levels in the river. Recently a study by the World Wide Fund for Nature (WWF) found that Ganga is one of the ten most endangered rivers in the world. The pollution levels have been rising for many years. This stage is reached because the towns and cities, through which the river flows, throw large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river. In fact the river is “dead” at many places where the pollution levels are so high that aquatic life cannot survive.

Question 16: Prepare a brief speech on global warming that you have to make in your class.

Answer: CO₂ is one of the gases responsible for this effect. Carbon dioxide is needed by plants. But if there is excess of CO₂ in the air, it acts as a pollutant. On the one hand, CO₂ is continuously being released because of human activities. On the other hand, area under forests is decreasing. Plants utilise CO₂ from the atmosphere for photosynthesis, thereby decreasing the amount of CO₂ in the air. Deforestation leads to an increase in the amount of CO₂ in the air because the number of trees which consume CO₂ is reduced. Human activities, thus, contribute to the accumulation of CO₂ in the atmosphere. CO₂ traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Question 17:  What are the harmful effects of water pollution?

Answer: Following are the harmful effects of water pollution:

• Water contaminated with sewage may contain bacteria, viruses, fungi and parasites which cause diseases like cholera, typhoid and jaundice.
• Excessive quantities of chemicals which get washed from the fields act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in the water body gets used up. This results in a decrease in the oxygen level which may kill aquatic organisms.
• Hot water released by power plants and industries raises the temperature of the water body and adversely affecting the animals and plants living in it.
• The chemicals released include arsenic, lead and fluorides which lead to toxicity in plants and animals.

Question 18: What are the main sources of air pollution?
Or
How does air get polluted?

Answer: Sources of air pollution

• Natural sources like smoke and dust arising from forest fires or volcanic eruptions cause air pollution.
• Pollutants are also added to the atmosphere by human activities. The sources of air pollutants are factories, power plants, automobile exhausts and burning of firewood and dung cakes.
• Pollutants like sulphur dioxide and nitrogen dioxide gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid and cause acid rain.
• Carbon monoxide is produced from the incomplete burning of fuels such as petrol and diesel. It is a poisonous gas.
• Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays cause air pollution.

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