Reaction of Phenol with conc. $HNO_3$ gives

Picric Acid

The correct answer is Option (2) → Picric Acid

Concept

Phenol is a highly activated aromatic compound due to the presence of the –OH group.

The –OH group is:

Strongly activating

Ortho–para directing

So, nitration occurs very easily.

What happens with Conc. HNO₃

With dilute HNO₃ → mono-nitration occurs (o-nitrophenol and p-nitrophenol)

With concentrated HNO₃ → strong nitration occurs

All three ortho and para positions get substituted.

Hence, 2,4,6-trinitrophenol is formed.

This compound is called Picric Acid.

Reaction:

Phenol + conc. HNO₃ → 2,4,6-Trinitrophenol (Picric Acid)

Explanation of Each Option

Option 1: Citric acid

Citric acid is an aliphatic carboxylic acid obtained from citrus fruits. It has no relation to nitration of phenol. Incorrect.

Option 2: Picric Acid

Concentrated nitric acid introduces three nitro groups at 2, 4, and 6 positions of phenol. Product formed = 2,4,6-trinitrophenol = Picric Acid. Correct.

Option 3: Nitrobenzene

Nitrobenzene is formed by nitration of benzene, not phenol. Phenol is more reactive and gives multi-substitution instead. Incorrect.

Option 4: o-Nitrobenzene

This is not even a correct compound name in this context. Mononitration product would be o-nitrophenol (with dilute acid). With conc. HNO₃, trinitration occurs instead. Incorrect.