${C_2}{H_5}I\,\xrightarrow{{Alc.\,KOH}}X\xrightarrow{{B{r_2}}}Y\xrightarrow{{KCN}}Z$
$(1)$ $CH_3CH_2-CH_2-OH$
$(2)$ $\begin{array}{*{20}{c}}
{C{H_3} - C{H_2} - CH - OH} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}}
\end{array}$
$(3)$ $\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\
\,\,\,\,\,\,|
\end{array}} \\
{C{H_3} - C{H_2} - C - OH} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}}
\end{array}$
$C{H_3}C{H_2}C \equiv CH\, + \,HCl\, \to \,B\,\xrightarrow{{HI}}C$