Question

Which of the following is not an air pollutant?
(A) $CO$
(B) $S{{O}_{2}}$
(C) $NO$
(D) ${{N}_{2}}$

Answer 1

An air pollutant is a substance which is harmful to the atmosphere and ultimately living organisms. Thus, one of the options in this question is not harmful to the atmosphere. Air pollutants are released from many vehicles and factories daily.

Complete answer:
The correct answer to this question is option D, ${{N}_{2}}$ (Nitrogen) is not an air pollutant. The atmosphere of earth is made up of 78% ${{N}_{2}}$ (Nitrogen), thus it cannot be an air pollutant otherwise there will be no life on earth.
An air pollutant is a substance (mostly gaseous) which is harmful for the atmosphere and the environment. Air pollutant is the name of the cause of air pollution, the substance which causes air pollution is known as air pollutant.
Air pollutants are mostly released from factories and from the exhaust of our vehicles. Our vehicles mainly emit carbon monoxide ( $CO$ ), and various nitrogen oxides ( $NOx$ ) with some other gases into the atmosphere. These gases are air pollutants.
The amount of air pollutants in the atmosphere has to be regulated. If proper care is not taken, it can be really harmful to the environment. Any gas that can harm the environment and pollute the air can be called an air pollutant.

Note:
Here, the other three gases shown in the question that are $CO$ (Carbon monoxide), $S{{O}_{2}}$ (Sulphur dioxide) and $NO$ (Nitrogen oxide) are air pollutants. All three gases are released from the exhaust of vehicles.