The product of the following substitution reaction is 

${\mathrm{CH}}_4+{\mathrm{Cl}}_2\stackrel{\mathrm{h\gamma }}{\to }?$

In the presence of sunlight, chlorine is added to hydrocarbons(alkane). Chlorine can replace by hydrogen atoms one by one. It is called a substitution reaction. Example: Methane reacts with chloride in the presence of sunlight to form Chloromethane and Hydrochloric acid.

${\mathrm{CH}}_4+{\mathrm{Cl}}_2\stackrel{\mathrm{h\gamma }}{\to }{\mathrm{CH}}_3\mathrm{Cl}+\mathrm{HCl}$