Chemistry Class-11: Chapter –14. Environmental Chemistry Part – 3

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III. Short Answer Type

Question: 17

Greenhouse effect leads to global warming. Which substances are responsible for greenhouse effect?


Trapping of heat by greenhouse gases, namely carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons.

Question: 18

Acid rain is known to contain some acids. Name these acids and where from they come in rain?


Question: 19

Ozone is a toxic gas and is a strong oxidising agent even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed?


[Hint: Ozone prevents harmful UV radiations of the Sun from reaching to the Earth’s surface, thereby it protects life from bad effects of UV radiations.]

Question: 20

Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?


Question: 21

On the basis of chemical reactions involved, explain how do chlorofluorocarbons cause thinning of ozone layer in stratosphere.


CFC’s are stable compounds. These undergo decomposition in presence of sunlight, as shown below:

Chain reactions continue in which ozone layer is depleted.

Question: 22

What could be the harmful effects of improper management of industrial and domestic solid waste in a city?


Question: 23

During an educational trip, a student of botany saw a beautiful lake in a village. She collected many plants from that area. She noticed that villagers were washing clothes around the lake and at some places waste material from houses was destroying its beauty. After few years, she visited the same lake again. She was surprised to find that the lake was covered with algae, stinking smell was coming out and its water had become unusable. Can you explain the reason for this condition of the lake?


[Hint: Process of eutrophication is responsible for this. Explain the effect of accumulation of phosphate from detergents and organic matter entering into the lake along with domestic waste.]

Question: 24

What are biodegradable and non-biodegradable pollutants?


Biodegradable - which are decomposed by bacteria.

Non-biodegradable - which cannot be decomposed by bacteria.

Question: 25

What are the sources of dissolved oxygen in water?


Sources of dissolved oxygen in water

(i) Photosynthesis

(ii) Natural aeration

(iii) Mechanical aeration

Question: 26

What is the importance of measuring BOD of a water body?


BOD is the measure of level of pollution caused by organic biodegradable material. Low value of BOD indicates that water contains less organic matter.

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