$HC\, \equiv \,CH\,\xrightarrow[{20\% \,{H_2}S{O_4}}]{{1\% \,HgS{O_4}}}A$ $\xrightarrow[{{H_2}O}]{{C{H_3}MgX}}B\xrightarrow{{[O]}}(C)$
(a) $C{H_3}\, - \,\,\mathop C\limits_{\mathop |\limits_{C{H_3}} } \, = \,\,C{H_2}\,\xrightarrow{{HBr}}\,\,C{H_3}\, - \,\,\mathop {\mathop C\limits_{\mathop |\limits_{C{H_3}} } }\limits^{\mathop |\limits^{Br} } \,\, - \,\,C{H_3}$
(b) $C{H_3}\, - \,\,CH\,\, = \,\,C{H_2}\,\mathop {\xrightarrow{{HBr}}}\limits_{Peroxide} \,\,C{H_3}\,C{H_2}\,C{H_2}\,Br$
(c) $C{H_4}\, + \,\,C{l_2}\,\xrightarrow{{hv}}\,\,C{H_3}Cl\,\, + \,\,HCl$
$\begin{array}{*{20}{c}}
{C{H_3} - C = CH - C{H_2}C{H_3}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{CH{{(C{H_3})}_2}\,\,\,\,\,\,\,\,\,\,}
\end{array}\xrightarrow[{(ii)\,{H_2}{O_2},O{H^ - }}]{{(i)\,{B_2}{H_6}}}[A]$$\xrightarrow[\Delta ]{{dil.\,{H_2}S{O_4}}}[B]$