Nitro group is an electron withdrawing group, so
increase the acidic character of phenol whereas −CH3 and −OCH3 both are electron releasing
groups, so it decrease the acidic character of phenol
but −CH3 group is less electron donating or
releasing, so p-methyl phenol is slightly more acidic
than p-methoxy phenol and p-nitro phenol is most
acidic, so the order of acidic character is
p-methoxy phenol < p-methyl phenol < p-nitro phenol.