Question

Why p-chloro benzoix acid is more acific than p-flouro benzoic acid?

Answer 1

Both group chloro and floro shows inductive effect generally.

But

When they attached to benzene like structure or in resonance condition then,They start showing 'Mesomeric effect'.

Mesomeric effect is more influential than inductive and mesomeric effect of chlorine is more than that of fluorine Hence Chlorine will stabilize the compound more than florine.

Hence Acidic character is more in p-chloro Benzoic Acid. than p-floro Benzoic Acid.