A) Dissolved oxygen (DO) in cold water can reach a concentration up to 10 ppm.
B) Clean water would have a BOD value of 5 ppm.
C) Fluoride deficiency in drinking water is harmful. Soluble fluoride is often used to bring its concentration up to 1 ppm.
D) When the pH of rain water is higher than 6.5, it is called acid rain.
Correct Answer: D
Solution :
Acid rain is the rain water containing sulphuric acid and nitric acid, which are formed from the oxides of sulphur and nitrogen present in the air as pollutants and rain water has a pH of 4-5.
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