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.

Answer: Option (iii), (iv)
Solution: (i) A pH of rainwater being 5.6 is not necessarily an indicator of a polluted environment.
This is because rainwater naturally has a pH of around 5.6 due to the presence of carbon dioxide in the atmosphere, which reacts with water to form carbonic acid. However, if the pH of rainwater is significantly lower than 5.6, it could be an indicator of acid rain, which is a form of pollution caused by emissions of sulfur dioxide and nitrogen oxides.
(ii) An amount of carbon dioxide in the atmosphere being 0.03% is not necessarily an indicator of a polluted environment. This is because carbon dioxide is a naturally occurring gas in the atmosphere and is necessary for the survival of plants. However, if the concentration of carbon dioxide in the atmosphere is significantly higher than normal, it could be an indicator of air pollution caused by human activities such as burning fossil fuels.
(iii) Biochemical oxygen demand (BOD) of 10 ppm is an indicator of a polluted environment. BOD is a measure of the amount of oxygen required by microorganisms to break down organic matter in water. A high BOD indicates that there is a large amount of organic matter in the water, which can lead to oxygen depletion and harm aquatic life.
(iv) Eutrophication is also an indicator of a polluted environment. Eutrophication is a process in which a body of water becomes enriched with nutrients, such as nitrogen and phosphorus, which can lead to excessive growth of algae and other aquatic plants. This can cause oxygen depletion and harm aquatic life. Eutrophication is often caused by human activities such as agricultural runoff and sewage discharge.

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