Q27 / 180 · AIIMS 2015 · Botany

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

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

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 $20^{\circ} \mathrm{C}$ 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 $20^{\circ} \mathrm{C}$ should not be more than $20 \mathrm{ppm}$, i.e., 20 mg per litre.

Hence, the correct answer is option: 'A'.

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