Methemoglobinemia is due to

Excess nitrate in drinking water can cause

Given below are two statements:
Statement $I$: Chlorofluorocarbons breakdown by radiation in the visible energy region and release chlorine gas in the atmosphere which then reacts with stratospheric ozone.
Statement $II$: Atmospheric ozone reacts with nitric oxide to give nitrogen and oxygen gases,which add to the atmosphere.
For the above statements choose the correct answer from the options given below :

An increase in $CO_2$ concentration in the atmosphere will result in

Which type of pollution is caused by the spraying of $DDT$ on crops?

The normal rain water is slightly acidic and its $pH$ value is $5.6$ because of which one of the following?