The compound that undergoes decarboxylation most readily is 

For the above sequence of reactions, identify the correct statements.
(a) $\mathrm{A}$ has more $\mathrm{pKa}$ than $\mathrm{D}$.
(b) $\mathrm{B}$ can be prepared by the deamination of m-toluidine.
(c) $\mathrm{A}$ and $\mathrm{D}$ show HVZ reaction.
(d) $\mathrm{A}$ can be prepared from $\mathrm{D}$ by reduction with ${\mathrm{H}}_2, {\mathrm{CuCr}}_2{\mathrm{O}}_4$.

In the above reaction, $\mathrm{C}$ is

The compound given below is used as

The major product is