But$-1-$ene reacts with $\mathrm{HBr}$ in the presence of peroxide and forms ______.

The reaction is:

${\text{R-CH}}_{\text{2}}\text{-OH + HCl }\stackrel{}{\to }{\text{R-CH}}_{\text{2}}{\text{-Cl+H}}_{\text{2}}\text{O}$

For the completion of the reaction, ______ is used.

In the reaction;

$\mathrm{X}+{\mathrm{PCl}}_{\mathrm{5}}\mathrm{ }\stackrel{\mathrm{\Delta }}{\to }{\mathrm{CH}}_{\mathrm{3}}{\mathrm{CH}}_{\mathrm{2}}\mathrm{Cl}+{\mathrm{POCl}}_{\mathrm{3}}$, $\mathrm{X}$ is ______.