Removal of the soil by the action of wind and water is known as

The concentration of dissolved oxygen in water for the growth of fish should be more than $X \ ppm$ and the Biochemical Oxygen Demand $(BOD)$ in clean water should be less than $Y \ ppm$. $X$ and $Y$ in $ppm$ are,respectively:

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

The gaseous component present in the troposphere is ...... .

In drinking water,if the maximum prescribed concentration of copper is $x \ mg \ dm^{-3}$,the maximum prescribed concentration of zinc will be

Pollution can be controlled by