CBSE Class 8 Science Pollution of Air and Water VBQs

Question. Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer : D

Question. What are the different ways in which water gets contaminated?
Answer : Following are the ways by which water gets contaminated:
• People dispose of garbage in the water.
• Many industries discharge their harmful chemicals directly into rivers and streams.
• Chemical fertilizers, pesticides and weedicides used in agricultural practices get dissolve in water and are washed away into water bodies from the fields.
• Untreated sewage is directly discharged into water from household activities.

Question. Describe the threat to the beauty of the Taj Mahal.
Answer :The major threat to the Taj Mahal is the acid rain. Acid rain corrodes the marble of Taj Mahal and makes it yellowish. This is a matter of great concern that world famous monument like Taj Mahal may get damaged due to the pollutants emitted by factories around it.

Question. Clear, transparent water is always fit for drinking. Comment.
Answer : No, this is not true that clean, transparent water is always fit for drinking. It is possible that they may carry disease-causing microorganisms and other transparent impurities.

Question. Explain circumstances leading to acid rain. How does acid rain affect us?
Answer : Gases like sulphur dioxide and nitrogen dioxide react with water vapour present in atmosphere to form Sulphuric acid and nitric acid. These acids come down with rain water, making the rain acidic. This is known as acid rain. 
Acid rain corrodes the marbles of the monuments. It also kills the useful organism in agricultural soil.

Question. 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 : The following steps could be taken:
(a) First of all, procurement of required amount of water for all residents should be ensured.
(b) Wastage of water by leakage at various places should be taken into account.
(c) Water treatment should be ensured.
(d) Must have sufficient water tanker to meet emergency situations.

Question. Explain the differences between pure air and polluted air.
Answer : Pure air is free from any pollutant, has no smell, is soothing and not irritating to eyes. Whereas polluted air gives a filthy smell and people cannot breathe in it. If people inhale such air, they may suffer from various breathing, heart and lung problems. Even sometimes people die inhaling polluted air.

Question. Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer : Good Morning,
Respected teacher and my dear friends,
As we all know the continuous increase in the temperature of earth is called global warming. Global warming is basically caused by pollution of air, excessive heat which is trapped by the greenhouse gases.
Global warming is a threat to life as it causes a lot of problems like droughts and fire. So we should plant more trees and should avoid air pollution.
Thanks.

Question. At an individual level, how can you help to reduce air pollution?
Answer : The following are the steps we can take for reduction of air pollution:
i) We should use public transport.
ii) We should properly dispose of the garbage and not burn it.
iii) For shorter distances, avoid vehicles.
iv) We should plant more trees.
v) We should replace our vehicle fuel, diesel and petrol by LPG and CNG.

Question. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer : Increased level of nutrients in the water affect the survival of aquatic organisms as these act as nutrients for algae to flourish and once these algae die, they serve as food for decomposers like bacteria and a huge amount of oxygen in water body gets used up. This results in decrease in the oxygen level, which may kill aquatic organisms.

Question. Describe the ‘Greenhouse Effect’ in your own words.
Answer : Gases like carbon dioxide and methane trap Sun’s radiation reflected from earth’s surface. This causes warming of atmosphere. This effect is called greenhouse effect.