Which of the following acids has the smallest dissociation constant (Ka)?

CH3CH(F)COOH FCH2CH2COOH BrCH2CH2COOH CH3CH(Br)COOH

BrCH2CH2COOH

Out of the four given species,BrCH2CH2COOH is least acidic and has the least dissociation constant (less Ka value). It is because of (i) the lesser -I effct of Br As compared to the F and (ii) Br atom is further away from the -COOH group.