Explanation

(b)
Electron withdrawing group has $–I$ effect while electron donating group has $+ I$ effect. In$\ CH_{3}COOH$, the alkyl group $\left( - CH_{3} \right)$ due to its greater $+ I$ effect increases the electron density on oxygen atom of the O-H bond. Due to this the release of $H^{+}$ ion in acetic acid will be more difficult as compared to formic acid.