Consider the following reaction and identify A and B.

A: Phenol-2,4-disulphonic acid; B: Picric acid

The correct answer is Option (1) → A: Phenol-2,4-disulphonic acid; B: Picric acid

Step 1: Reaction with concentrated $H_2SO_4$

Phenol undergoes sulphonation. In concentrated sulphuric acid and at elevated temperature, phenol forms phenol-2,4-disulphonic acid.

The $-OH$ group is strongly activating and ortho-para directing. Therefore, sulphonation occurs at ortho and para positions.

Thus A is phenol-2,4-disulphonic acid.

Step 2: Reaction with concentrated $HNO_3$

When phenol-2,4-disulphonic acid is treated with concentrated nitric acid, the $-SO_3H$ groups are replaced by $-NO_2$ groups.

This gives 2,4,6-trinitrophenol, commonly known as picric acid.

Thus B is picric acid.