Which of the following statements about the depletion of zone layer is correct ?

Question

(a) The problem of depletion is less serious at poles because $\;NO_{2}\;$ solidifies and is not available for consuming $\;CIO^{.}\;$ radicals (b) The problem of depletion is more serious at poles because ice crystals in the clouds over poles act as catalyst for photochemical reactions involving the decomposition of ozone by $\;CI^{.}\;$ and $\;CIO^{.}\;$ radicals (c) Frenos ,chlorofluorocarbons , are inert chemically ,they do not react with ozone in stratosphere (d) Oxides of nitrogen also do not react with ozone in stratosphere