Persons working in cement plants and limestone quarries are more prone to diseases like

Excess nitrate in drinking water can cause

Biochemical Oxygen Demand,$(BOD)$ is a measure of organic material present in water. $BOD$ value less than $5 \ ppm$ indicates a water sample to be ..... .

Mention the types of pollution.

What are biodegradable and non-biodegradable pollutants?

What do you mean by ozone hole? What are its consequences?