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Science class 8- Chapter 18- Pollution of air and water-Ncert Exercise Solution ( Question-Answer)

Science Class 8 – Chapter 18- Pollution of air and water– NCERT exercise solution (Question-Answer) is provided below. Total 11 Questions are in this NCERT Exercise, all are solved here

Exercise- Questions with Answers

Q1.  What are the different ways in which water gets contaminated?

Answer- Following are different ways in which water gets contaminated-

  • Disposal of garbage in the water.
  • Harmful chemicals from industries discharge directly into the river and streams.
  • Waste household material discharge in the water body.
  • Chemical fertilisers, pesticides and weedicides which is used in the crop production. These get carried away to water bodies due to rain and flood and hence lead to water pollution.

Q2. At an individual level, how can you help reduce air pollution?

Answer– An individual can reduce air pollution by-

  • Using public transport.
  • Generate awareness among people to reduce air pollution.
  • Using clean fuels. Examples- LPG, CNG in place of diesel and petrol.
  • Don’t burn garbage.
  • Controlling the emission from vehicles, chimneys, etc.

Q3. Clear, transparent water is always fit for drinking. Comment.

Answer– No, clean transparent water is not always fit for drinking because it may carry disease-causing microorganism. So, we should purify water before drinking.

Q4. 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- Following is the list of measures that would help our town to ensure the supply of clean water to all its residents.

  • The area around the water pipe must be clean.
  • Chlorination method must be used for purifying water.
  • Proper cleaning of the water tank.

Q5. Explain the differences between pure air and polluted air.


Pure air Polluted air
It contains 78% nitrogen, 21% oxygen, 0.03% carbon dioxide and other gases such as argon, methane, ozone and water vapour also present in a small quantity.When the addition of harmful gases such as nitrogen dioxide, sulphur dioxide, carbon mono-oxide, etc then air is said to be polluted.

Q6. Explain circumstances leading to acid rain. How does acid rain affect us?

Answer- Pollutant like nitrogen dioxide, sulphur dioxide react with water vapour present in atmosphere form sulphuric acid and nitric acid. These acids come in the rain and make rain acidic. This is called acid rain.

Reactions involved-

SO₂ (g) + H2O ——> H2SO₃

H2SO₃ + O₂ ——-> 2 H2SO4

Similarly,        2NO₂ + H2O ——> HNO₃ + HNO₂

2HNO₂ +O2 ——–>2HNO₃

Effects of acid rain-

  • Damage building and sculptural material.
  • Can cause a skin disease in human being.
  • It damages the crop.
  • Increase corrosion in metals.

Q7. Which of the following is not a greenhouse gas?

(a) Carbon dioxide

(b)  Sulphur dioxide

(c) Methane

(d) Nitrogen

Answer-(d) Nitrogen

Q8. Describe the ‘Green House Effect’ in your own words.

Answer- Greenhouse effect may lead to global warming, it means the increase in temperature of the earth. It is caused by greenhouse gases such as CO2, methane, etc.

When the sun rays fall on the surface of the earth, some of the radiations get absorbed by the earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and doesn’t allow to leave. This process helps in keeping our planet warm and thus help in survival.

But, if it will increase than normal, then our earth will get warmed than enough and this cause to global warming.

Q9. Prepare a brief speech on global warming. You have to deliver the speech in your class.

Answer- The continuous increase in the temperature of the earth is called as global warming caused by air pollution, excessive heat trapped by greenhouse gases etc. Due to trapping of heat by greenhouse gases makes the earth more heater and this is known as global warming. It can cause a lot of health problems with plants and animals. We may have to face dire consequences due to global warming.

Effects of global warming-

  • Melting glaciers, early snowmelt, and severe droughts
  • Rising sea levels will lead to coastal flooding
  • Disruption of habitats
  • Forests, farms, and cities will face troublesome new pests, heat waves, heavy downpours, and increased flooding.

Q10. Describe the threat to the beauty of the Taj Mahal.

Answer- Due to acid rain and pollution in the air, the colour of white marbles of Taj Mahal getting discolouring day by day. When acid rain falls on Taj Mahal, they react with marbles and form a powder-like substance that is then washed away by the rain. Suspended particulate matter such as soot particles emitted by Mathura Oil Refinery has contributed toward the yellowing of the marble.

Q11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer- The increased level of nutrients in the water affect the survival of aquatic organisms because it leads to an excessive increase in the population of algae in the water body. When the algae die, they are served as food for decomposers like bacteria and a huge amount of oxygen in water body gets used up. This cause a decrease in the oxygen level. By this, aquatic organisms may die.

Pollution of air and water Science class 8 Ncert Exercise Solution ended👍👍👍

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