Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	Photochemical smog is oxidizing in nature.
Reason (R):	Photochemical smog contains NO₂ and O₃, which are formed during the sequence of reactions.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere.

When fossil fuels are burnt, a variety of pollutants are emitted into the earth's troposphere. Two of the pollutants that are

emitted hydrocarbons (unburnt fuels) and nitric oxide (NO).

When these pollutants build up to sufficiently high levels, a chain reaction occurs from their interaction with sunlight in

which NO oxidizes to NO₂. This NO₂ in turn absorbs energy from sunlight and breaks up into nitric oxide and free oxygen

atom.

{NO}_{2} (g) \overset{hv}{\to} NO (g) + O (g)

Oxygen atoms are very reactive and combine with O₂ in the air to produce ozone.

O (g) + O_{2} (g) ⇌ O_{3} (g)