KCET 2025 Chemistry Paper

Trichloroacetic acid (Option C) is the strongest acid. Here's why:Electron-withdrawing effectChlorine atoms pull electron density away from the -COOH group, stabilizing the conjugate base (the carboxylate anion).More $\mathrm{Cl} \rightarrow$ greater stabilization $\rightarrow$ stronger acid. Comparative pKa valuesPropanoic acid, $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{COOH}$ : $\mathrm{pKa} \approx 4.87$Chloroacetic acid, $\mathrm{ClCH}_2 \mathrm{COOH}$ : pKa $\approx 2.86$Dichloroacetic acid, $\mathrm{Cl}_2 \mathrm{CHCOOH}$ : pKa $\approx 1.25$Trichloroacetic acid, $\mathrm{CCl}_3 \mathrm{COOH} : \mathrm{pKa} \approx 0.66$ Since trichloroacetic acid has the lowest pKa, it donates its proton most readily and is thus the most acidic.