b
$CH_3CHO$ $+$ $H_3CCHO$ (એસિટાલ્ડીહાઇડ ) $ \xrightarrow {NaOH}$ $\begin{array}{*{20}{c}}{\,\,\,\,\,OH\,\,\,\, \,\,\,\, \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\,\,\,\, \,\,\,\, \\ {C{H_3} - CH - C{H_2}C{H_3}CHO} \end{array}\,\,\,$ (આલ્ડોલ)