Explanation

(b)
$- Cl$ is an electron withdrawing (i.e.,$- I$ showing) group. It withdraws electrons when attached to the carboxylic acid and decreases the electron density on the oxygen atom. This will facilitate the release of $H^{+}$ by making $O - H$ bond more polar and thus $–Cl$ increases the acidity of acetic acid when attached at, $\alpha$ position because of $–I$ effect.