Identify[A],[B] and[C], respectively in the following reaction sequence:

Solution

Chemistry ma’am · 4 steps

Read each arrow as a named reaction: diazotisation, then iodide swap, then Fittig coupling.

1. Find A. NaNO₂ and HCl at 273 to 278 K is diazotisation. Only a primary aromatic amine gives a diazonium salt this way, so A is aniline, C₆H₅NH₂.
2. Find B. Warming the diazonium salt with KI replaces -N₂⁺ with iodine, and N₂ gas escapes. No copper catalyst is needed for iodide. So B is iodobenzene, C₆H₅I. The Cl⁻ is only the counter ion and does not end up on the ring.
3. Find C. Sodium in dry ether joins two aryl halide molecules through a new C–C bond. This is the Fittig reaction.

   2C₆H₅I + 2Na →(dry ether) C₆H₅-C₆H₅ + 2NaI

4. So. A is aniline, B is iodobenzene and C is biphenyl, which is option (c).

The idea to keep. The group that replaces -N₂⁺ comes from the reagent on the arrow, never from the counter ion. And Na in dry ether always couples two aryl halides: that is Fittig.

Answer from the NTA final answer key. Solution by PrepWiser.