NCERT Solutions Science Chapter 18 Pollution of Air and Water for Class 8th

Question 1.
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 fertilisers, 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 2.
At an individual level, how can you help to reduce air pollution?
Answer:
I can do the following things to reduce air pollution:

• I will use public transport as far as possible.
• I will generate awareness among people to reduce air pollution.
• I will plant more and more trees because trees help to keep the environment clean and reduce air 1 pollution.
• I will not use vehicles for short distances.

Question 3.
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. Thus, it is good to purify water before 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:
These are the measures that would help our town to ensure the supply of clean water to all its residents:

• Chlorine tablets should be made available.
• Proper cleaning of the water tank from time to time.
• The water supply pipes should not come in contact with the sewage pipes.

Question 5.
Explain the differences between pure air and polluted air.
Answer:
Pure air contains 78% nitrogen, 21% oxygen and 0.03% C02. Other gases such as argon, methane, neon, water vapour, etc. are also found in small quantities. When this air is contaminated by unwanted substances which have harmful effect on both living and non-living things like nitrogen oxide, sulphur oxide, carbon monoxide, etc., is said to be polluted.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer:
Nitrogen dioxide, sulphur dioxides are the pollutants which react with the water vapour present in atmosphere to form sulphuric acid and nitric acid. These acids come down with the rain, making the rain acidic. This is called acid rain.
Following are the affects of acid rain:

• It increases corrosion of metals.
• It damages buildings and sculptural materials.
• It removes the basic nutrients such as calcium from the soil.
• It causes direct damage to plants and crops.
• It causes skin eruptions in human being.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer:
(d) Nitrogen

Question 8.
Describe the ‘Greenhouse Effect’ in your own words.
Answer:
Basically, the greenhouse effect means warming of the earth’s environment. When the sun’s ray falls on earth, a part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus helps in survival. CO2, methane and CO are the gases responsible for this effect.

Question 9.
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 health problems. We may have to face dire consequences due to global warming.
That’s all friends. Thank you for the attention. Have a good day.

Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer:
Taj Mahal has become a matter of concern due to pollutants in air that are discolouring its white marble. Acid rains due to increasing air pollution has started corroding the marble. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble. Thus making Taj Mahal losing its beauty.

Question 11.
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.