Chemistry - GOC Question with Solution | TestHub

All three chlorobenzoic acids are stronger than benzoic acid because chlorine withdraws electron density by its -I effect. The effect is strongest closest to the COOH group, and at the ortho position the COOH is also forced out of the ring plane, cutting off the ring's electron-donating resonance (ortho effect). Hence o-chlorobenzoic acid (II) is the most acidic ($\mathrm{p}{K}_{\mathrm{a}}$ : II 2.94 $<$ III 3.83 $<$ IV 3.99 $<$ I 4.20).