JEE Main 2025 Jan 29 Shift 2, Chemistry Q16: Diazonium Salt

An azo dye contains the $-N=N-$ linkage between two aromatic rings, typically built by diazotisation of an aromatic primary amine followed by coupling with an electron-rich aromatic such as a phenol or naphthol.

Tracing option (1):

$PhN{O}_2\stackrel{Sn/HCl}{\to }PhN{H}_2\stackrel{NaN{O}_2/HCl,0-5^{\circ }C}{\to }Ph{N}_2^{+}C{l}^{-}\stackrel{\beta \text{-naphthol/NaOH}}{\to }$ 1-(phenylazo)-2-naphthol.

The final product carries the azo group between phenyl and naphthyl rings and is the classic orange azo dye.

The other sequences either form amides, anilides or simple ring substitutions, none of which generate an $-N=N-$ linkage.

$\therefore$ Option (1) is the correct route.