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Question

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Assertion: BOD of a river polluted by sewage is more than 20 ppm.
Reason: Polluted river contains excess of organic matter.

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

Solution

A.

If both assertion and reason are true and reason is the correct explanation of assertion.

Degree of impurity of water due to organic matter is measured in terms of BOD (Biochemical oxygen demand). BOD is the oxygen in milligrams required for five days in one litre of water at 20°C for the microorganisms to metabolise organic waste. It is measured in the milligrams of oxygen taken up in one litre of sewage. The effluent that is legally allowed to be discharged into a river or stream should be such that BOD at 20°C should not be more than 20 ppm, i.e., 20 mg per litre.

Some More Questions From Environmental Issues Chapter

WHO’s recommendations about the industrial noise limit is of :

Which of the atmospheric layer contains ozone layer ?

The amount of dissolved oxygen required by the microorganisms to degrade the organic wastes present in water is called ?

The cause of acid rain is :

Which one of the following causes ozone depletion ?

What disease is caused due to consumption of fishes captured from water contaminated with mercury ?

Which one of the following is not a green-house gas ?

Which gas contributes the maximum in global warming ?

Fill in the blanks with suitable words :
1. Increase in concentration of soluble salts in the soil is called.........

2. Aforestation can check the advancement of......... .

3. DDT is a serious pollutant as it is a.........pollutant and undergoes......... .

4 .........plant has become a troublesome weed in agricultural fields.

5 .........are major aerosol pollutant present in jet aircraft emission.

Write “True” or “False” :

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