Ethanamine is treated with $\mathrm{NaNO}{}_2/\mathrm{HCl}$ at $273\mathrm{K}$ to give A, and A is oxidised with PCC to give B. B is

Aliphatic primary amines react with nitrous acid to give the alcohol, with evolution of $\mathrm{N}{}_2$: $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{NH}{}_2$ gives $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{OH}$ (A). PCC oxidises a primary alcohol only as far as the aldehyde, giving $\mathrm{CH}{}_3\mathrm{CHO}$ (B).