The correct sequential order of the reagents for the given reaction is

Solution

Chemistry ma’am · 4 steps

Swap the existing NH₂ for I first, then turn NO₂ into a new NH₂ and swap that for OH.

1. Map the groups. In p-nitroaniline, the NH₂ position ends up as I and the NO₂ position ends up as OH. Both swaps go through a diazonium salt, and only an NH₂ group can be diazotised.
2. Iodine first. HNO₂ (from NaNO₂ + HCl at 0 to 5 °C) turns NH₂ into -N₂⁺. A diazonium salt is unstable, so it is trapped at once with KI, which gives p-iodonitrobenzene.
3. Make a new amine. Fe/H⁺ reduces NO₂ to NH₂, which gives p-iodoaniline. This new amine group is now ready for a second diazotisation.

   O₂N-C₆H₄-NH₂ →(HNO₂, KI) O₂N-C₆H₄-I →(Fe/H⁺) H₂N-C₆H₄-I →(HNO₂, H₂O, warm) HO-C₆H₄-I

4. So. A second dose of HNO₂ gives the diazonium salt, and warming it with water replaces N₂⁺ by OH. The order is HNO₂, KI, Fe/H⁺, HNO₂, H₂O/warm, which is option (b).

The idea to keep. Two groups to install by diazotisation? Use the existing NH₂ first and trap its diazonium salt at once. Only then reduce NO₂ to NH₂ for the second round.

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