(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) $C{H_4}\, + \,\,C{l_2}\,\xrightarrow{{hv}}\,\,C{H_3}Cl\,\, + \,\,HCl$