${CH}_{4}+{I}_{2} \underset{\text { Reversible }}{\stackrel{{hv}}{\longrightarrow}} {CH}_{3}-{I}+{HI}$
It can be irreversible in the presence of strong oxidising agent like conc. ${HNO}_{3}$ or conc. ${HIO}_{3}$




$\begin{array}{*{20}{c}}
{C{H_3}\,\,\,} \\
{|\,\,\,\,\,\,\,\,} \\
{C{H_3} - C - CHC{H_3}} \\
{\,|\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,H\,\,\,\,\,\,\,Br}
\end{array}$ $\xrightarrow{{C{H_3}OH}}$