Question

Depletion of the ozone layer is due to

• A. None of the above
• B. Oxides of nitrogen
• C. Oxides of carbon
• D. Oxides of sulphur

Answer 1

The correct option is B Oxides of nitrogen

Ozone layer
Oxides of nitrogen lead to ozone depletion. This is because it results in the formation of chlorine sinks. These after hydrolysis or reaction with HCl produces hypochlorous acid. This in turn gives rise to free chlorine radicals. The chlorine radicals initiate a chain of reactions resulting in ozone degradation.
${\text{ClO}}^{\cdot }+{\text{NO}}_2\to {\text{ClONO}}_2$
${\text{Cl}}^{\cdot }+{\text{CH}}_4\to {\text{CH}}_3^{\cdot }+\text{HCl}$
${\text{ClONO}}_2+{\text{H}}_2\text{O}\to \text{HOCl}+{\text{HNO}}_3$
${\text{ClONO}}_2+\text{HCl}\to {\text{Cl}}_2+{\text{HNO}}_3$
$\text{HOCl}\to \cdot \text{OH}+{\text{Cl}}^{\cdot }$
${\text{Cl}}_2\to 2{\text{Cl}}^{\cdot }\to$ Initiate chain of reactions leading to ozone depletion

Final answer
Ozone layer
Oxides of nitrogen lead to ozone depletion. This is because it results in the formation of chlorine sinks. These after hydrolysis or reaction with HCl produces hypochlorous acid. This in turn gives rise to free chlorine radicals. The chlorine radicals initiate a chain of reactions resulting in ozone degradation.
${\text{ClO}}^{\cdot }+{\text{NO}}_2\to {\text{ClONO}}_2$
${\text{Cl}}^{\cdot }+{\text{CH}}_4\to {\text{CH}}_3^{\cdot }+\text{HCl}$
${\text{ClONO}}_2+{\text{H}}_2\text{O}\to \text{HOCl}+{\text{HNO}}_3$
${\text{ClONO}}_2+\text{HCl}\to {\text{Cl}}_2+{\text{HNO}}_3$
$\text{HOCl}\to \cdot \text{OH}+{\text{Cl}}^{\cdot }$
${\text{Cl}}_2\to 2{\text{Cl}}^{\cdot }\to$ Initiate chain of reactions leading to ozone depletion

Final answer
(A) Oxides of nitrogen