Which of the following solvents reduces the environmental pollution?

Assertion : Photochemical smog is produced by nitrogen oxides.
Reason : Vehicular pollution is a major source of nitrogen oxides.

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:

Which of the following are considered atmospheric air pollutants?

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

What percentage of the total atmosphere is occupied by the homosphere?