c
Given, \(\mathrm{CH}_{3} \mathrm{COOH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{H}^{+}\)

\(K_{a}=1.5 \times 10^{-5} \ldots \ldots .(i)\)

\(H C N \rightleftharpoons H^{+}+C N^{-}, K_{a 1}=4.5 \times 10^{-6} \ldots \ldots(i i)\)

For \(\mathrm{CN}^{-}+\mathrm{CH}_{3} \mathrm{COOH} \rightleftharpoons \mathrm{HCN}+\mathrm{CH}_{3} \mathrm{COO}^{-}\)

\(K=?\)

On subtracting Eq. \((ii)\) from Eq. \((i)\), we get

\(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CN}^{-} \rightleftharpoons \mathrm{HCN}+\mathrm{CH}_{3} \mathrm{COO}^{-}\)

\(k=\frac{K_{e}}{K_{a_{1}}}=\frac{1.5 \times 10^{-5}}{4.5 \times 10^{-10}}\)

\(=\frac{10^{5}}{3}=3.33 \times 10^{4}\)

\(\approx 3 \times 10^{4}\)