Which of the following compounds comprise of a phenolic group?

(A) Salicylic acid
(B) Salicylaldehyde
(C) Cresol
(D) Catechol

Choose the correct answer from the options given below:

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

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

A phenolic group means an $-\text{OH}$ group directly attached to a benzene ring. The compound may also contain other functional groups $(-\text{COOH, } -\text{CHO, } -\text{CH}_3)$, but as long as an $-\text{OH}$ is bonded to the aromatic ring, it is phenolic.

Explanation (option-wise)

(A) Salicylic acid

It is o-hydroxybenzoic acid. The $-\text{OH}$ is directly attached to the benzene ring along with a $-\text{COOH}$ group. Hence, it contains a phenolic $-\text{OH}$.

(B) Salicylaldehyde

This is o-hydroxybenzaldehyde. The benzene ring has both $-\text{CHO}$ and $-\text{OH}$ groups, and the $-\text{OH}$ is phenolic in nature.

(C) Cresol

Cresol is methyl phenol ($-\text{CH}_3$ and $-\text{OH}$ on benzene). The hydroxyl group is attached directly to the aromatic ring, so it is a phenol derivative.

(D) Catechol

Catechol is benzene-1,2-diol. It has two $-\text{OH}$ groups directly attached to the ring, so it definitely contains phenolic groups.