Write structures of compounds $A, B$ and $C$ in each of the following reaction: (i) $\mathrm{C}_6\mathrm{H}_5\mathrm{Br} \xrightarrow{\mathrm{Mg} / \text{ dry ether }} A \xrightarrow[\text{ (b) } \mathrm{H}_3\mathrm{O}^+]{(a) \mathrm{CO}_{2(g)}} B \xrightarrow{\mathrm{PCl}_3} C$ $B \xrightarrow{\mathrm{PCl}_3} C$ (ii) $\mathrm{CH}_3\mathrm{CN} \xrightarrow[\text{ (b) } \mathrm{H}_3\mathrm{O}^+]{(a) \mathrm{SnCl}_2 / \mathrm{HCl}} A \xrightarrow{\text{ dil. } \mathrm{NaOH}} B$ $\xrightarrow{\Delta} \text{ C }$ OR Do the following conversions in not more than two steps: (i) Benzoic acid to benzaldehyde (ii) Ethyl benzene to benzoic acid (iii) Propanone to propene