b
\({C_2}{H_5}I\xrightarrow{{{\text{alc}}.{\kern 1pt} KOH}}{C_2}{H_4}\xrightarrow{{B{r_2}}}\) \(\begin{array}{*{20}{c}}
  {C{H_2} - C{H_2}} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,} \\ 
  {Br\,\,\,\,\,\,\,\,\,\,\,\,\,Br\,\,\,} 
\end{array}\)

\(\xrightarrow{{KCN}}\) \(\mathop {\begin{array}{*{20}{c}}
  {C{H_2} - C{H_2}} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,} \\ 
  {CN\,\,\,\,\,\,\,\,\,CN} 
\end{array}}\limits_{{\text{Butene  -  1, 4  -  dinitrile}}} \)