Identify the correct structure of a yellow dye.

The correct answer is Option (1) → p-Aminoazobenzene, C₆H₅–N=N–C₆H₄–NH₂(p)

Benzene diazonium chloride couples with aniline at the para position to give p-aminoazobenzene, the yellow azo dye known as aniline yellow:

    \( \displaystyle \ce{C6H5N2^+Cl^- + C6H5NH2 -> C6H5-N=N-C6H4-NH2 + HCl} \)

• Option (2) p-chloroazobenzene — Incorrect. p-Chloroazobenzene is not aniline yellow, and chlorobenzene is too unreactive to couple with a diazonium ion.

• Option (3) p-bromoazobenzene — Incorrect. For the same reason it is not a coupling product of a diazonium salt; bromobenzene does not couple.

• Option (4) p-hydroxyazobenzene — Incorrect. It is formed by coupling with phenol and is an orange dye, not the yellow one.

NCERT (2026-27 edition):
Reactions Involving Retention of Diazo Group – “… The azo products obtained have an extended conjugate system having both the aromatic rings joined through the –N=N– bond. These compounds are often coloured and are used as dyes. Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to form p-hydroxyazobenzene. This type of reaction is known as coupling reaction. Similarly the reaction of diazonium salt with aniline yields p-aminoazobenzene. This is an example of electrophilic substitution reaction.”