Assertion (A): If BOD level of water in a reservoir is less than 5 ppm it is highly polluted.
Reason (R): High biological oxygen demand means a low activity of bacteria in water.
(i) Both A and R are correct and R is the correct explanation of A.
(ii) Both A and R are correct but R is not the correct explanation of A.
(iii) Both A and R are not correct.
(iv) A is not correct but R is correct.
The answer is the option (iii) Both A and R are not correct.
Explanation: BOD is a measure of the amount of organic material present in water, in terms of how much oxygen it requires to break it down biologically. If the water has a value of BOD less than 5 ppm, it is considered as clean water; however, water pollution increases if the BOD increases.