NEET2015BotanyEnvironmental IssuesActual
Assertion : BOD of a river polluted by sewage is more than 20 ppm . Reason : Polluted river contains excess of organic matter.
Options
- AIf both assertion and reason are true and reason is the correct explanation of assertion.
- BIfboth assertion and reason are true but reason is not the correct explanation of assertion.
- CIf assertion is true but reason is false.
- DIf both assertion and reason are false.
Correct answer
A. If both assertion and reason are true and reason is the correct explanation of assertion.
Step-by-step solution
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 B O D at 20^ C should not be more than 20 ppm , i.e., 20 mg per litre.