JAMB Chemistry 2011 Paper

Concept:This is a free-radical substitution reaction of an alkane with chlorine, which is initiated by light.Explanation:The reaction $\mathrm{CH}_{4(g)} + \mathrm{Cl}_{2(g)} \rightarrow \mathrm{CH}_3\mathrm{Cl}_{(g)} + \mathrm{HCl}_{(g)}$ proceeds by a free-radical mechanism.The chlorine molecule $\mathrm{Cl}_2$ splits into chlorine free radicals only when exposed to ultraviolet light.Therefore, the major factor influencing the rate of this reaction is light.Answer:D. light