Which of the following reaction/s will not give $$p$$-aminoazobenzene?

We need to determine which reaction(s) will not give $$p$$-aminoazobenzene.

Reaction A: Nitrobenzene is first reduced with Sn/HCl to give aniline. Then treatment with $$HNO_2$$ (i.e., $$NaNO_2 + HCl$$) converts aniline to benzenediazonium chloride. Finally, coupling with aniline (a weakly activating group) gives $$p$$-aminoazobenzene. This reaction works correctly.

Reaction B: Nitrobenzene is treated with $$NaBH_4$$. However, $$NaBH_4$$ is a mild reducing agent that cannot reduce nitrobenzene to aniline. $$NaBH_4$$ is typically used for reducing aldehydes, ketones, and acid chlorides, not nitro groups. Reduction of nitrobenzene requires stronger reducing agents like Sn/HCl, Fe/HCl, or catalytic hydrogenation. Since aniline is not formed, the subsequent steps to make $$p$$-aminoazobenzene will not proceed. This reaction does not give the desired product.

Reaction C: Aniline is treated with $$HNO_2$$ (diazotization) to form benzenediazonium chloride, which then undergoes coupling with aniline in the presence of HCl to give $$p$$-aminoazobenzene. This is the standard method and works correctly.

Therefore, only reaction B will not give $$p$$-aminoazobenzene, which corresponds to option (1).