In the Rosenmund reduction, the catalyst used is:

In the following reaction identify compounds $\mathrm{A}, \mathrm{B}, \mathrm{C}$ and $\mathrm{D} :$

${\mathrm{PCl}}_5+{\mathrm{SO}}_2⟶\mathrm{A}+\mathrm{B}$

$\mathrm{A}+{\mathrm{CH}}_3\mathrm{COOH}⟶\mathrm{C}+{\mathrm{SO}}_2+\mathrm{HCl}$

$2\mathrm{C}+{\left({\mathrm{CH}}_3\right)}_2\mathrm{Cd}⟶\mathrm{D}+{\mathrm{CdCl}}_2$

What are $\mathrm{A}$ and $\mathrm{B}$ in the following sequence of reactions:

$\left(\mathrm{i}\right)$ ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COOH}\underset{{\mathrm{Br}}_2}{\overset{\mathrm{P}}{\to }}\mathrm{A}$

$\left(\mathrm{ii}\right) \mathrm{A}\underset{\left(\mathrm{ii}\right) {\mathrm{H}}^{+}}{\overset{\left(\mathrm{i}\right) \mathrm{Alc}.\mathrm{KOH} \mathrm{excess}}{\to }}\mathrm{B}$

Identify $\mathrm{B},\mathrm{X}$ and $\mathrm{R}$ respectively in the following sequence of reactions

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{MgBr}\stackrel{\mathrm{CCN}}{⟶}\mathrm{A}\stackrel{{\mathrm{H}}_3{\mathrm{O}}^{+}}{⟶}\boxed{\mathrm{B}}$

${\mathrm{CH}}_3{\mathrm{COCH}}_3\underset{\mathrm{NaOH}}{\overset{{\mathrm{I}}_2}{\to }}\boxed{\mathrm{X}}\stackrel{\mathrm{Ag}}{⟶}\mathrm{Y}$

${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2\underset{\mathrm{HCl}}{\overset{{\mathrm{NaNO}}_2}{\to }}\mathrm{P}\stackrel{\mathrm{CuCN}}{\to }\mathrm{Q}\stackrel{+4\mathrm{H}}{\to }\boxed{\mathrm{R}}$