$C{H_3}C{H_2}C \equiv CH\, + \,HCl\, \to \,B\,\xrightarrow{{HI}}C$
${CH}_{4}+{I}_{2} \underset{\text { Reversible }}{\stackrel{{hv}}{\longrightarrow}} {CH}_{3}-{I}+{HI}$