Which of the following conditions shows the polluted enviorment ?

Options

A. pH of rain water 5.6
B. Amount of carbon dioxide in the atmosphere is `0.03%`
C. Biochemical oxygen demand `10 "ppm"`
D. Eutrophication

Answer

C, D

Explanation

Polluted water may contain nutrients for the growth of algae, which covers the water surface and reduces the oxygen concentration in water. This leadsd to anaerobic condition, accumlation of abnoxious decay and animal death. This is process of eutrophication.
The amount of oxygen by bacteria to break down the oxigin Demand. Clean water would have BOD value of `5 "ppm"` whereas highly polluted could have BOD value of `17"ppm"` or more.
Normally rain water has pH of `6` due to `H^(+)` ion formed by reaction of rain water with carbon dioxides in the atmosphere. When the pH of the rain water drops below 5.6, it is called acid rain.