Arrange the following phenols in the decreasing order of their acidic strength:

(A) Phenol
(B) o-Cresol
(C) o-Nitrophenol
(D) 2,4-Dinitrophenol

Choose the correct answer from the options given below:

(D), (C), (A), (B)

The correct answer is Option (2) → (D), (C), (A), (B)

In substituted phenols, the presence of electron withdrawing groups such as nitro group, enhances the acidic strength of phenol. This effect is more pronounced when such a group is present at ortho and para positions. It is due to the effective delocalisation of negative charge in phenoxide ion. On the other hand, electron releasing groups, such as alkyl groups, in general, do not favour the formation of phenoxide ion resulting in decrease in acid strength. Cresols, for example, are less acidic than phenol.

Phenols in decreasing order of their acidic strength

2,4-dinitrophenol > o-nitrophenol > phenol > o-cresol