Question: Phenol, on heating with conc. $\text{HNO}_3$, gives :

Step 1 (Governing Chemical Principle): [0.5 Mark]

The reaction of phenol with concentrated nitric acid ($\text{conc. HNO}_3$) in the presence of concentrated sulfuric acid ($\text{conc. H}_2\text{SO}_4$) is an electrophilic aromatic substitution reaction known as nitration. When phenol is treated with concentrated $\text{HNO}_3$, the nitronium ion ($\text{NO}_2^+$) acts as the electrophile, leading to the substitution of hydrogen atoms at the 2, 4, and 6 positions of the benzene ring.

Step 2 (Step-by-Step Reaction Mechanism): [0.25 Mark]

The reaction proceeds as follows:

$$ \text{C}_6\text{H}_5\text{OH} + 3\text{HNO}_3 \xrightarrow{\text{conc. H}_2\text{SO}_4} \text{C}_6\text{H}_2(\text{NO}_2)_3\text{OH} + 3\text{H}_2\text{O} $$

The product formed is 2,4,6-trinitrophenol, commonly known as Picric acid. The strong oxidizing nature of concentrated nitric acid ensures that substitution occurs at all available ortho and para positions simultaneously.

Step 3 (Final Concluded Answer): [0.25 Mark]

The correct option is (C) Picric acid.

💡 EL10 Concept Insight: Think of phenol as a very "inviting" house for the nitro groups; because it is so reactive, when you use strong concentrated acid, it lets three nitro groups move in at once at the 2, 4, and 6 positions, creating the explosive compound known as Picric acid.