When ${\mathrm{CHCl}}_3$ is boiled with $\mathrm{NaOH}$, it gives

The following reaction,

$\mathrm{R}-\mathrm{X}+\mathrm{NaI}\to \mathrm{R}-\mathrm{I}+\mathrm{NaX}$  where, $\mathrm{X}=\mathrm{Cl},\mathrm{Br}$ is known as