The correct option is C Major constituent of photochemical smog is SO2
Classical smog occurs in cold and humid climate. It is a mixture of smoke, fog and SO2.
Chemically it is reducing in nature.
Photochemical smog occurs in warm, dry and sunny climate. It is oxidising in nature due to presence of high concentration of oxidising agents. Major constituents of photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories.