Among the acids (i) Butyric acid (ii) 2 -chlorobutyric acid (iii) 3-chlorobutyric acid (iv) 2 -dichlorobutyric acid The acidic strength increases on. (i) Presence of electron with drawing group. (i.e. - I group) (ii) Closeness of electron withdrawing group from the −COOH groups. (iii) Number of electron with drawing groups. (i.e. - I group) Hence, the correct order will be I<III<II<IV