The chlorination of methane in the presence of ultraviolet light proceeds by

Explanation

Ultraviolet light splits the chlorine molecule homolytically into two radicals, which then abstract hydrogen from methane and set up a chain reaction of propagation steps until two radicals combine and terminate it. Because the chain continues, the reaction does not stop at chloromethane but produces a mixture of all four chlorinated products. Substitution is characteristic of saturated compounds, while addition belongs to unsaturated ones.