Pure ${\mathrm{CHCl}}_3$ and pure ${\mathrm{CHI}}_3$ can be distinguished by

Identify $z$ in the following series

${\mathrm{CH}}_2={\mathrm{CH}}_2\underset{\mathrm{\Delta }}{\overset{\mathrm{HBr}}{\to }}\mathrm{x}\stackrel{\mathrm{Hydrolysis}}{\to }\mathrm{y}\stackrel{{\mathrm{I}}_2/\mathrm{NaOH}}{\to }\mathrm{z}$

Identify $\mathrm{D}$ :-