Which of the following statements is correct?
(i) Ozone hole is a hole formed in the stratosphere from which ozone oozes out.
(ii) Ozone hole is a hole formed in the troposphere from which ozone oozes out.
(iii) Ozone hole is thinning of the ozone layer of the stratosphere at some places.
(iv) Ozone hole means vanishing of the ozone layer around the earth completely.
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Ans: Option (iii) Ozone hole is thinning of the ozone layer of the stratosphere at some places is correct since it was found that a unique set of conditions were responsible for the ozone hole. In summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks, preventing much ozone depletion, whereas in winter, special types of clouds called polar stratospheric clouds are formed over Antarctica.
Following reactions occur in the stratosphere.
\[\text{C}{{\text{F}}_{\text{2}}}\text{C}{{\text{l}}_{\text{2}}}\to \text{C}{{\text{F}}_{\text{2}}}\text{Cl+}\overset{\bullet }{\mathop{\text{Cl}}}\,\]
\[\overset{\bullet }{\mathop{\text{Cl}}}\,\text{+}{{\text{O}}_{\text{3}}}\to \text{Cl}\overset{\bullet }{\mathop{\text{O}}}\,\text{+}{{\text{O}}_{\text{2}}}\]
\[\text{Cl}\overset{\bullet }{\mathop{\text{O}}}\,+\text{ }\!\![\!\!\text{ O }\!\!]\!\!\text{ }\to \overset{\bullet }{\mathop{\text{Cl}}}\,+{{\text{O}}_{\text{2}}}\]