KCET 2018 Chemistry Solved Paper

Presence of −NO2 group increases the acidic character of phenol, because it is an electron withdrawing group, it withdraws the electron towards itself thereby decreasing the e− density on the conjugate base so formed and stabilizes by resonance, whereas the electron releasing groups increases the e− density on conjugate base and destabilizes it. Therefore, the increasing order of acidic strength is : I < II < III.