A cyclic compound that gives succinic acid on oxidative cleavage is-

Which of the following acids will undergo decarboxylation easily?

${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}\stackrel{{\mathrm{PCl}}_5}{⟶}\mathrm{A}+{\mathrm{POCl}}_3+\mathrm{HCl}$ . Compound $\mathrm{A}$ can also be formed by treating chlorine with the following compound in the absence of a halogen carrier-

Which of the following decolourises the colour of acidic ${\mathrm{KMnO}}_4$?

In the Cannizzaro reaction given below,

 $2\mathrm{PhCHO} \stackrel{\stackrel{\mathrm{\Theta }}{\mathrm{O}}\mathrm{H}}{\to }{\mathrm{PhCH}}_2\mathrm{OH}+{\mathrm{PhCO}}_2^{\Theta }$, the slowest step is :