The cyanohydrin of a carbonyl compound on hydrolysis gives lactic acid. The carbonyl compound is:

Consider the following sequence of reactions:

$\mathrm{PhC}=\mathrm{CH}\underset{\mathrm{dil}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\overset{{\mathrm{HgSO}}_4}{\to }}\mathrm{A}\stackrel{{\mathrm{NH}}_2\mathrm{OH}}{\to }\mathrm{B}+\mathrm{C}$

The products $\left(\mathrm{A}\right), \left(\mathrm{B}\right)$ and $\left(\mathrm{C}\right)$ are respectively:

The major product formed in the reaction is:

${\mathrm{C}}_{\mathrm{g}}{\mathrm{H}}_5\mathrm{CHO}+{\mathrm{CH}}_3{\mathrm{NO}}_2\underset{\mathrm{heat}}{\overset{\mathrm{NaOH}}{\to }}\left(\mathrm{X}\right)$

Identify product $\left(\mathrm{B}\right)$ in the following reaction sequence: