Environmental Chemistry - Result Question 13
13. The molecule that has minimum/no role in the formation of photochemical smog, is
(a) $N _2$
(b) $CH _2=O$
(c) $NO$
(d) $O _3$
(2019 Main, 12 Jan I)
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Answer:
Correct Answer: 13. (a)
Solution:
- $N _2$ molecule has minimum role in the formation of photochemical smog. While $CH _2=O, O _3$ and $NO$ has major role. When fossil fuels are burnt, a variety of pollutants are emitted. Two of them are hydrocarbons (unburnt) and NO. When these pollutants build upto high levels, a chain reaction occurs from their interaction with sunlight. The reactions involved in the formation of photochemical smog are as follows:
$$ \begin{gathered} \mathrm{NO}_2(g) \xrightarrow{h v} \mathrm{NO}(g)+\mathrm{O}(g) \\ \mathrm{O}(g)+\mathrm{O}_2(g) \rightleftharpoons \mathrm{O}_3(g) \\ \mathrm{NO}(g)+\mathrm{O}_3(g) \longrightarrow \mathrm{NO}_2(g)+\mathrm{O}_2(g) \end{gathered} $$ $\mathrm{O}_3$ reats with unburnt hydrocarbons to produce chemicals such as formaldehyde, acrolein and PAN. $$ \begin{aligned} & \text { } \ & \end{aligned} $$
$3 \mathrm{CH}_4+2 \mathrm{O}_3 \longrightarrow 3 \mathrm{CH}_2=\mathrm{O}+3 \mathrm{H}_2 \mathrm{O}$
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