Arrange the following in increasing acidic character

Phenol, m- nitrophenol, m – chlorophenol, m- cresol

    (i)    (ii)         (iii)         (iv)

Here the substitutes are present in m – position, so they will not show any mesomeric effect; only inductive effect operates, $-N{O}_2$ group has + charge on N, so it has more electron – with drawing inductive effect than Cl; m – nitrophenol will be more acidic than m – chlorophenol. Methyl group is acid – weakening group. Hence the relative acidic strength is

m- cresol < phenol < m – chlorophenol < m – nitrophenol

IV I III II