What happens when methane reacts with chlorine?

Methane is an alkane with the chemical formula, ${\mathrm{CH}}_4$

When methane reacts with chlorine, a substitution reaction occurs and the organic product obtained is chloromethane.
${\mathrm{CH}}_4 + {\mathrm{Cl}}_2 \to \underset{\mathrm{Chloromethane}}{{\mathrm{CH}}_3\mathrm{Cl}}$
However, the reaction does not stop there, followed by other reactions in which all hydrogen atoms in methane are replaced by chlorine atoms. 

This means at the end, we get chloroform $\left({\mathrm{CH}}_3\mathrm{Cl}\right)$, dichloromethane $\left({\mathrm{CH}}_2{\mathrm{Cl}}_2\right)$, trichloromethane $\left({\mathrm{CH}}_2{\mathrm{Cl}}_2\right)$, and carbon tetrachloride $\left({\mathrm{CCl}}_4\right)$.

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

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

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

${\mathrm{CHCl}}_3+{\mathrm{Cl}}_2\to {\mathrm{CCl}}_4$

These reactions proceed via a free radical chain reaction mechanism.

Hence option (B) is correct.