Answer: KI.
- A Cu<sub>2</sub>Cl<sub>2</sub>/HCl
- B H<sub>3</sub>PO<sub>2</sub>
- C CuCN/KCN
- D KI
Correct answer: D. KI
Explanation: Unlike -Cl or -Br, the iodo group is introduced by warming the diazonium salt with potassium iodide, no copper needed.
In aniline, the nitrogen's lone pair is pulled into the benzene ring through resonance, leaving less electron density available to accept a proton - which is why aniline is a much weaker base than methylamine, where the lone pair is fully available.
Concept context
Nitrogen-containing organic compounds. Covers classification (primary, secondary, tertiary), basicity comparison, preparation methods, and reactions including diazotization and coupling, key for understanding dyes and pharmaceuticals.