The percent composition of an organic compound $\underline{\mathrm{A}}$ is carbon : 85.71% and hydrogen 14.29%. Its vapour density is 14. Consider the following reaction sequence :

$\underline{\mathrm{A}} \stackrel{\mathrm{C}{1}_2/{\mathrm{H}}_2\mathrm{O}}{\to } \underline{\mathrm{B}} \underset{\left(2\right){\mathrm{H}}_3{\mathrm{O}}^{+}}{\overset{\left(1\right)\mathrm{KCN}/\mathrm{EtOH}}{\to }} \underline{\mathrm{C}.}$ Identify $\underline{\mathrm{C}}.$

$$\begin{gathered} \mathrm{C} \mathrm{H} \\ 85.71 14.29 \\ \frac{85.71}{12} \frac{14.29}{1} \\ \frac{7.14 }{7.14} \frac{ 14.29}{7.14} \\ \mathrm{C}:\mathrm{H}=1:2 \\ \mathrm{E}.\mathrm{F}={\mathrm{CH}}_2 , \mathrm{Its} \mathrm{wt}.=14 \\ \mathrm{Given} \mathrm{VD}=14, \mathrm{Mol}. \mathrm{Wt}.=2\times 14=28 \\ \mathrm{n}=\frac{28}{14}=2 \\ \mathrm{M}.\mathrm{F}={\left({\mathrm{CH}}_2\right)}_2={\mathrm{C}}_2{\mathrm{H}}_4 \end{gathered}$$

$$\begin{gathered} \mathrm{Now}, \\ {\mathrm{CH}}_2={\mathrm{CH}}_2\stackrel{{\mathrm{Cl}}_2/{\mathrm{H}}_2\mathrm{O}}{\to } {\mathrm{CH}}_2\left(\mathrm{Cl}\right)-{\mathrm{CH}}_2\left(\mathrm{OH}\right)\underset{\left(2\right){\mathrm{H}}_3{\mathrm{O}}^{+}}{\overset{\left(1\right)\mathrm{KCN}/\mathrm{EtOH}}{\to }} \\ {\mathrm{CH}}_2\left(\mathrm{OH}\right)-{\mathrm{CH}}_2-{\mathrm{CO}}_2\mathrm{H} \end{gathered}$$