18. Pollution of Air and Water Science class 8 in English Medium ncert book solutions Text Book Exercise

Exercise - Question:

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

Ans: 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.

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

Ans: 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.

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

Ans: 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.

Que: 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.

Ans: 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.

Que: Explain the differences between pure air and polluted air.

Ans: 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.

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

Ans: 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.

Que: Which of the following is not a greenhouse gas?

(a) Carbon dioxide

(b) Sulphur dioxide

(c) Methane

(d Nitrogen

Ans: (d) Nitrogen|