The reaction is called $\begin{array}{*{20}{c}}
{2C{H_3} - C - O{C_2}{H_5}} \\
{||\,\,\,} \\
{O\,\,\,}
\end{array}$ ${\xrightarrow{{{C_2}{H_5}ONa}}}$ $\begin{array}{*{20}{c}}
{C{H_3} - C - C{H_2} - C - O{C_2}{H_5}} \\
{||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||\,\,\,\,\,\,\,} \\
{O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O\,\,\,\,\,}
\end{array}$ $ + \,{C_2}{H_5}OH$
→The number of sigma bonds in $\begin{array}{*{20}{c}} {{{\rm{H}}_3}{\rm{C}} - {\rm{C}} = {\rm{CH}} - {\rm{C}} \equiv {\rm{C}} - {\rm{H}}}\\ {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\ {H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \end{array}$ is $......$
→