b
\({C_2}{H_5}I{\mkern 1mu} {\mkern 1mu} \xrightarrow[{KOH}]{{alc.}}{\mkern 1mu} {\mkern 1mu} \mathop {{C_2}{H_4}}\limits_{(X)} {\mkern 1mu} \) \(\xrightarrow{{B{r_2}}}{\mkern 1mu} {\mkern 1mu} C{H_2}Br - C{H_2}Br{\mkern 1mu} \) \(\xrightarrow{{KCN}}\)\(\begin{array}{*{20}{c}}
{C{H_2} - C{H_2}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,} \\
{CN\,\,\,\,\,\,\,\,\,\,\,CN\,}
\end{array}\)