Answer the question on the basis of the passage given below:
Molecular nitrogen is very little reactive chemically. During lightning discharge, atmospheric nitrogen and oxygen combine to form nitric oxide which also combines with oxygen to form nitrogen dioxide. Both \(NO\) and \(NO_2\) constitute smog which is very poisonous. It can cause a burning sensation in the eyes and adversely affect the respiratory system.
What are the constituents of photochemical smog?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Photochemical smog are oxide of nitrogen, organic compounds like formaldehyde acrolein and peroxyacetyl nitrate (PAN)
Smog is of two kinds:
Classical smog (cool, humid climate): smoke, fog and sulphur dioxide; it is reducing in nature.
Photochemical smog (warm, dry, sunny climate): formed when sunlight acts on oxides of nitrogen and hydrocarbons from vehicle exhaust; it is oxidising in nature.
In photochemical smog, \( \ce{NO2} \) splits in sunlight, and the oxygen atoms form ozone; ozone and the nitrogen oxides then react with the unburnt hydrocarbons. The common components are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate (PAN).
So the correct description is oxides of nitrogen together with formaldehyde, acrolein and PAN.
Why the other options are incorrect
Option (2) oxide of nitrogen, organic compounds like formalin acrolein and PAN — Incorrect. Formalin is the 40% solution of formaldehyde in water, used as a preservative; the smog contains formaldehyde gas, not formalin.
Option (3) oxide of sulphur, organic compounds like formalin acrolein and PAN — Incorrect. Oxides of sulphur belong to classical smog, and formalin is a solution, not a smog gas.
Option (4) oxide of sulphur, organic compounds like formaldehyde acrolein and PAN — Incorrect. The organic part is right, but photochemical smog is built on oxides of nitrogen; sulphur dioxide is the gas of classical smog.