Answer: 4-nitrophenol.
- A phenol
- B 4-methylphenol
- C 4-nitrophenol
- D 4-methoxyphenol
Correct answer: C. 4-nitrophenol
Explanation: The electron-withdrawing nitro group at the para position stabilises the phenoxide ion, making 4-nitrophenol the strongest acid here.
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.