Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	If the BOD level of water in a reservoir is less than 5 ppm it is highly polluted.
Reason (R):	High biological oxygen demand means the low activity of bacteria in water.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	Both (A) and (R) are false.

Hint: The BOD value of clean water would be less than or equal to 5 ppm.

The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called Biochemical Oxygen Demand (BOD).

If the BOD level is less than 5 ppm, water is almost pure. High biological oxygen demand means the high activity of bacteria in water.

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