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

Which of the following is the product of the above reaction?

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

The product formed is ${\mathrm{CH}}_3\mathrm{Cl}$.  A substitution reaction takes place. 

Substitution reaction is the process in which one or more hydrogen atoms from a hydrocarbon are replaced by another atom. A saturated hydrocarbon's defining trait is substitution reaction (alkanes).
Example: Chlorine and methane combine with sunlight to create chloromethane and HCl.