Answer: Concentrated HNO3.
- A Dilute HNO3
- B Concentrated HNO3
- C Br2 water
- D NaOH
Correct answer: B. Concentrated HNO3
Explanation: Concentrated nitric acid converts phenol into 2,4,6-trinitrophenol (picric acid).
The phenoxide ion's negative charge spreads into the aromatic ring through resonance, lowering its energy and making phenol give up its proton more easily; an alkoxide ion (from a plain alcohol) has nowhere to delocalise the charge, making alcohols far less acidic.
Concept context
Oxygen-containing organic compounds. Understand the acidic nature of phenols, reactions of alcohols (dehydration, oxidation, esterification), and properties of ethers. Includes industrial applications and named reactions.