Trichloroacetic acid (Option C) is the strongest acid. Here's why: Electron-withdrawing effect Chlorine atoms pull electron density away from the -COOH group, stabilizing the conjugate base (the carboxylate anion). More Cl⟶ greater stabilization ⟶ stronger acid. Comparative pKa values Propanoic acid, CH3CH2‌COOH : pKa≈4.87 Chloroacetic acid, ClCH2‌COOH : pKa ≈2.86 Dichloroacetic acid, Cl2‌CHCOOH : pKa ≈1.25 Trichloroacetic acid, CCl3‌COOH:pKa≈0.66 Since trichloroacetic acid has the lowest pKa, it donates its proton most readily and is thus the most acidic.