a
\(CH_3CHO\) \(+\) \(H_3CCHO\) \(\xrightarrow {NaOH}\) \(\mathop {\begin{array}{*{20}{c}}
{OH\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{C{H_3} - CH - C{H_2} - CHO}
\end{array}}\limits_{\beta \,\, - \,\,hydroxy\,\,butanal} \) \(\xrightarrow {-H_2O,\,\,\Delta ,\,\,dil acid}\) \(\mathop {C{H_3}CH = CH - CHO}\limits_{(krotonaldyhide)} \)