Question

Among the following compounds, which one is not responsible for the depletion of the ozone layer?
a.) \[C{{H}_{4}}\]
b.) \[CFC{{l}_{3}}\]
c.) NO
d.) \[C{{l}_{2}}\]

Answer 1

Hint: The main cause of ozone layer depletion is the existence of chlorine containing gases like CFCs, related halocarbons and oxides of nitrogen.
CFCs- Chlorofluorocarbons.
They deplete the ozone layer through the formation of free radicals in presence of sunlight.

Complete step by step answer:
In the presence of UV light, halogen containing gases dissociate and generate free radicals of chlorine.
The formed chlorine free radical then goes on to catalyze the destruction of the ozone layer.

Coming to the given options, option B, \[CFC{{l}_{3}}\]
\[CFC{{l}_{3}}\xrightarrow{hv}CFCl_{2}^{\centerdot }+C{{l}^{\centerdot }}\]
\[CFC{{l}_{3}}\] Undergoes homolytic cleavage and forms chlorine free radical. The chlorine free radical in the above reaction reacts with ozone and depletes the ozone layer.
Hence methane is not responsible for the depletion of the ozone layer.

Coming to option C, NO.
\[2NO\xrightarrow{hv}{{N}_{2}}+2{{O}^{\centerdot }}\]
The formed oxygen free radical in the above reaction reacts with ozone and depletes the ozone layer.

Coming to option D, \[C{{l}_{2}}\]
\[C{{l}_{2}}\xrightarrow{hv}2C{{l}^{\centerdot }}\]
Coming to option A,\[C{{H}_{4}}\]. Methane does not undergo free radical reaction in presence of sunlight.
Therefore the chemical which does not deplete the ozone layer among the given options is methane.
So, the correct answer is “Option A”.

Note: The depletion of the ozone layer by the chlorine and oxygen free radical is as follows.
\[\begin{align}
  & {{O}_{3}}+C{{l}^{\centerdot }}\to {{O}_{2}}+Cl{{O}^{\centerdot }} \\
 & Cl{{O}^{\centerdot }}+{{O}_{3}}\to Cl{{O}_{2}}+{{O}_{2}} \\
\end{align}\]

In the above reaction chlorine free radical reacts with ozone and forms oxygen and \[Cl{{O}^{\centerdot }}\]free radical. The formed \[Cl{{O}^{\centerdot }}\]further reacts with one more ozone and converts into oxygen and\[Cl{{O}_{2}}\]. It is a chain reaction, it continues further.
\[{{O}_{3}}+{{O}^{\centerdot }}\to 2{{O}_{2}}\]

In the above reaction oxygen free radical formed from NO when exposed to sunlight reacts with ozone and forms oxygen as the product.