Class 8 Science

Pollution of Air and Water

NCERT Solution

Question 1: What are the different ways in which water gets contaminated?

Answer: Water gets contaminated by following:

Question 2: At an individual level, how can you help reduce air pollution?

Answer: I can take following steps to reduce air pollution:

Question 3: Clear, transparent water is always fit for drinking. Comment.

Answer: Even the clear, transparent water may contain harmful germs. Thus the clear water is not necessarily fit for drinking.

Question 4: 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: I will take following steps to ensure the supply of clean water:

Question 5: Explain the differences between pure air and polluted air.


Pure airPolluted air
All the gases are in correct ratio.Harmful gases are in higher ratio.
No SPMs in air.High level of SPMs in air.
Smog is absent.Smog can be present.
It is not harmful for living beings.It is harmful for living beings.

Question 6: Explain circumstances leading to acid rain. How does acid rain affect us?

Answer: When oxides of nitrogen and sulphur mix with rainwater, they form acids. It results in acid rain, i.e. the rainwater becomes acidic. Acid rain is very harmful for living beings. Acid rain also damages buildings and monuments.

Question 7: Which of the following is not a greenhouse gas?

  1. Carbon dioxide
  2. Sulphur dioxide
  3. Methane
  4. Nitrogen

Answer: (d) Nitrogen

Question 8: Describe the Green House Effect in your own words.

Answer: Some gases trap solar radiation which helps in increasing the temperature of the atmosphere. This effect is called greenhouse effect.

Question 9: Prepare a brief speech on global warming that you have to make in your class.

Answer: Global warming is a serious concern of the modern times. We are using more cars and bikes than past. We are also consuming at a large scale which means more and more factories are coming up to satisfy our greed. All of this has resulted in an increased level of carbon dioxide in the atmosphere. The increased level of carbon dioxide has resulted in global warming.

Due to this; the summers have become hotter and winters have become much colder. We are seeing increased instances of flash floods. Weather changes are drastic and this is being attributed to global warming.

Global warming would result in total disaster for us. A time will come when the temperature on the earth will finish the life as we know it.

It is high time we should stand up and take a pledge to fight against global warming.

Question 10: Describe the threat to the beauty of the Taj Mahal.

Answer: Taj Mahal is made up of white marble. Marble is composed of calcium carbonate. Calcium carbonate reacts with acids and thus gets corroded. This is the reason; acid rain is damaging the Taj Mahal. This wonderful monument does not look white but is looking pale and dull. If corrective measures are not taken, the future generations may not be able to see the beauty of the Taj.

Question 11: Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer: Increased level of nutrients in water helps in promoting the growth of algae. Algae proliferate quickly to cover the whole water body. This phenomenon is called algal bloom. Finally, when these algae die; many decomposers thrive in the water body to decompose the dead algae. Increased population of decomposers means a lot of oxygen in the water gets utilised by them. This leaves less oxygen for other aquatic plants and animals. Thus, the aquatic plants and animals perish in the process.