Question

The reaction that is not involved in the ozone layer depletion mechanism in the stratosphere is
1. \(C{{H}_{4}}+2{{O}_{3}}\to 3C{{H}_{2}}=O+3{{H}_{2}}~O\)
2. \(C1\dot O\left( g \right) + O\left( g \right) \to \dot Cl\left( g \right) + {O_2}\;\left( g \right)\)
3. \(HOCl\left( g \right)\mathop \to \limits^{hv} \dot OH\left( g \right) + \dot Cl\left( g \right)\)
4. \(C{F_2}\;C{l_2}\;\left( g \right)\mathop \to \limits^{hv} \dot Cl\;\left( g \right) + \dot C{F_2}\;Cl\left( g \right)\)

Answer 1

Correct Answer - Option 1 : \(C{{H}_{4}}+2{{O}_{3}}\to 3C{{H}_{2}}=O+3{{H}_{2}}~O\)

Concept:

CH₄ is not present in the stratosphere and also it cannot diffuse or escape into the stratosphere like freon- 12

(CF₂ Cl₂) From the atmosphere. In the stratosphere, ozone layer depletion take place mainly by chlorofluorocarbons (CFCs) like CF₂ Cl₂ and the mechanism of ozone layer depletion can be shown as:

(i) \({\rm{C}}{{\rm{F}}_2}{\rm{C}}{{\rm{l}}_2}\left( g \right)\mathop \to \limits^{{\rm{hv}}} {\rm{C\dot l}}\left( g \right) + \dot C{{\rm{F}}_2}{\rm{Cl}}\left( g \right)\) [option d)]

(ii) \({\rm{C\dot l}}\left( {\rm{g}} \right) + {{\rm{O}}_3}\left( g \right) \to {\rm{Cl}}{{\rm{O}}^.}\left( g \right) + {{\rm{O}}_2}\) 

(iii) \({\rm{Cl}}{{\rm{O}}^.}\left( g \right) + {\rm{O}}\left( g \right) \to {\rm{Cl}}{{\rm{O}}^.}\left( g \right) + {{\rm{O}}_2}\) [option d]

(iv) \(C\dot l\left( g \right) + {H_2}O\;\left[ {present\;in\;the\;stratosphere} \right] \to HOCl\left( g \right) + {H^.}\left( g \right)\)

(v) \(HOCl\left( g \right)\mathop \to \limits^{hv} \;\dot OH\left( g \right) + C{l^.}\left( g \right)\) [option c]

⇒ One Cl^. can destroy or deplete 10⁵ O₃ molecule.

As (i) reaction is involved in the formation of photochemical smog, not in ozone layer depletion. So, option (a) is correct.