Environmental Chemistry · Question 12

Which one of the following statements is not true?

1. pH of drinking water should be between 5.5–9.5.
2. Concentration of DO below 6 ppm is good for the growth of fish.
3. Clean water would have a BOD value of less than 5 ppm.
4. Oxides of sulphur, nitrogen and carbon are the most widespread air pollutants.

Answer

(2) Concentration of DO below 6 ppm is good for the growth of fish.

Solution

As per NCERT, the pH of drinking water should be between 5.5 and 9.5, so (1) is true.

As per NCERT, if the concentration of dissolved oxygen (DO) in water is below 6 ppm, the growth of fish gets inhibited, so (2) is not true.

Clean water would have a BOD value of less than 5 ppm, whereas highly polluted water has 17 ppm or more, so (3) is true.

Oxides of sulphur, nitrogen and carbon are the most widespread air pollutants, so (4) is true.

Answer: (2)