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Answer
Correct option: C.$C{H_2} = CH - CHO$
c
$\underset{Glycerol}{\mathop{\begin{matrix}
\begin{matrix}
\begin{matrix}
H \\
| \\
\,\,\,\,H-C-OH \\
\end{matrix} \\
| \\
HO-C-H\,\,\,\, \\
| \\
\end{matrix} \\
H-C-H \\
| \\
\,\,\,\,\,OH \\
\end{matrix}}}$ $\xrightarrow{KHS{{O}_{4}}}$ $\underset{Unstable}{\mathop{\begin{matrix}
\begin{matrix}
\begin{matrix}
\,\,\,H\,\,\,\,\,\,\, \\
\,\,\,|\,\,\,\,\,\,\, \\
H-C\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
\,\, \,||\,\,\,\,\,\,\,\,\, \\
\,\,C\,\,\,\,\,\,\,\,\, \\
|\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
\,\,\,\,C-H \\
|\,\,\,\,\,\,\,\,\,\, \\
OH\,\,\,\, \\
\end{matrix}}}\,$ $\to $ $\underset{Unstable}{\mathop{\begin{matrix}
\begin{matrix}
\begin{matrix}
\,\,\,H\,\,\,\,\,\,\, \\
\,\,\,|\,\,\,\,\,\,\, \\
H-C\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
\,\,\,||\,\,\,\,\,\,\,\,\, \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C-H\,\,\,\,\,\,\,\,\, \\
\,\,\,||\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
\,\,\,\,\,C-H \\
\,\,\,||\,\,\,\,\,\,\,\,\,\, \\
\,\,O\,\,\,\,\,\,\,\,\,\, \\
\end{matrix}}}\,$ Or $\underset{Acrolein}{\mathop{\begin{matrix}
\begin{matrix}
C{{H}_{2}}\,\, \\
||\,\,\,\,\,\,\,\,\, \\
\end{matrix} \\
CH\,\,\,\, \\
|\,\,\,\,\,\,\,\,\, \\
CHO \\
\end{matrix}}}\,$