2,6-Dimethylbenzoic acid (pKa 3.25) is a considerably stronger acid than 4-methylbenzoic acid (pKa 4.37) in water. The best explanation is that

1. Athe two ortho methyl groups twist $\mathrm{COOH}$ out of the plane of the ring, which removes resonance stabilisation of the undissociated acid (steric inhibition of resonance)
2. Bthe $+I$ effect of the ortho methyl groups stabilises the carboxylate ion
3. Chyperconjugation from the ortho methyl groups withdraws electrons from $\mathrm{COOH}$
4. Dthe ortho methyl groups form an intramolecular hydrogen bond with $\mathrm{COOH}$