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Question
Which of the following conditions shows the polluted environment.
(i) pH of rain water is 5.6.
(ii) amount of carbondioxide in the atmosphere is 0.03%.
(iii) biochemical oxygen demand 10 ppm.
(iv) eutrophication.
Solution
(iii) biochemical oxygen demand 10 ppm.
(iv) eutrophication.
Explanation:
Polluted water may contain nutrients for the growth of algae, which covers the water surface and reduces the oxygen concentration in water. This leads to anaerobic condition, accumulation of obnoxious decay and animal death. This is process of eutrophication.
The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of sample of water is called Biochemical Oxygen Demand. Clean water would have BOD value of 5 ppm whereas highly polluted could have BOD value of 17 ppm or more.
Normally rain water has pH of 6 due to H+ ion formed by reaction of rain water with carbon dioxide in the atmosphere. When the pH of the rain water drops below 5.6, it is called acid rain.
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