a
\(\mathop {Br - \mathop {CH = }\limits^1 \mathop {CH}\limits^2 - Br}\limits_{\,\,\,s{p^2}\,\,\,\,\,\,s{p^2}} \,\mathop {\xrightarrow{{{H_2}}}}\limits_{{\text{Catalyst}}} Br - \mathop {C{H_2}}\limits_{s{p^3}}^{3\,\,\,\,\,} - \mathop {\mathop {C{H_2}}\limits^{4\,\,\,\,\,\,} }\limits_{s{p^3}} - Br\)