Explanation:
$\begin{matrix}
\begin{matrix}
C{{H}_{2}}OH \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
CHOH\,\, \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
C{{H}_{2}}OH \\
\end{matrix}$ $\xrightarrow[{ - \,3\,{H_2}O}]{{3HI}}$ $\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,C{H_2}I} \\
{\,|\,\,\,\,\,\,\,\,}
\end{array}} \\
{CHI} \\
{\,|\,\,\,\,\,\,\,\,} \\
{\,\,\,C{H_2}I}
\end{array}}\limits_{(high\,\,unstable)} $ $\xrightarrow[{ - \,{I_2}}]{}$ $\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{C{H_2}\,\,\,} \\
{||\,\,\,\,\,\,\,\,\,\,}
\end{array}} \\
{CH\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,} \\
{C{H_2}I\,\,}
\end{array}}\limits_{allyl\,\,iodide} $ $\xrightarrow{{HI\,\,(excess)}}$ $\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,\,\,C{H_3}} \\
{|\,\,}
\end{array}\,\,\,\,\,\,} \\
{CHI\,\,} \\
{\,|\,\,\,\,\,\,\,\,\,\,} \\
{C{H_2}I}
\end{array}}\limits_{(unstable)} $ $\xrightarrow[{ - \,{I_2}}]{}$ $\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{C{H_3}} \\
{|\,\,\,\,\,\,}
\end{array}} \\
{CH\,\,\,} \\
{||\,\,\,\,\,\,\,} \\
{C{H_2}}
\end{array}$ $\xrightarrow{{HI}}$ $\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{C{H_3}} \\
{|\,\,\,\,\,\,\,}
\end{array}} \\
{CHI} \\
{|\,\,\,\,\,\,\,} \\
{C{H_2}}
\end{array}}\limits_{2\, - \,iodopropane} $