8th std science pollution of air and water chapter question paper in english version 2020-21

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

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

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

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.

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

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

7. Which of the following is not a greenhouse gas? (a)  Carbon dioxide

(b)  Sulphur dioxide

(c)  Methane

(d)  Nitrogen

8.   Describe the ‘Greenhouse Effect’ in your own words.

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

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

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

1. Water gets contaminated by the addition of: (i)   Agricultural chemicals

(ii)  Industrial wastes

(iii) Sewage wastes

2. An individual can help reduce air pollution by: (i)   By usage of public transport

(ii)  By not using vehicles for short distances.

(iii) By using clean fuels such as LPG and CNG instead of diesel and petrol.

(iv) By disposing the garbage properly and not burning it.

(v)  By controlling the emissions from vehicles and household chimneys.

3. No, clear, transparent water is not always fit for drinking because of  the presence  of  microorganisms  causing harmful  diseases. Hence, we need to purify water before drinking.

4. To ensure the supply of clean water to all residents the following steps must be taken:

(i)   The main water source must be maintained properly by building it in clean surroundings.

(ii)  In purifying water, chemical methods like chlorination should be used. 

(iii) Water pipes must be maintained properly.

5. Pure air is a mixture of nitrogen, oxygen and carbon dioxide with other traces of gases like ozone, methane water vapour. When the composition of air is altered by addition of harmful gases like Sulphur dioxide, carbon monoxide, nitrogen dioxide and CFC’s, then the air is said to be polluted.

6. Burning of fossil fuels containing traces of Sulphur and trapped impurities  release  gases  like  Sulphur  dioxide  and  nitrogen dioxide.  Which  reacts  with  water  vapour  of  the  atmosphere forming respective acids like sulphurous acid. Which results in acid rain.

Effects of acid rain:

(i)   Acid rains damage crops.

(ii)  Acid rains corrode buildings and structures. Example: Taj

Mahal, Eiffel Tower are maintained in a span of time.

7.   (d) Nitrogen.

8. Greenhouse  effect  is  caused  by  greenhouse  gases  include carbon dioxide, methane, CFC’s which are released into atmosphere. The gases increase the temperature of the atmosphere by trapping radiation (i.e. not allowing the dissipation of  heat).  The increase in temperature  causes  global  warming leading to melt down of glacier in arctic and Antarctic regions increasing the sea level causing flooding and natural disasters.