Which one of the following reaction sequences will give an azo dye?

Azo dye synthesis requires diazotization followed by coupling:

Option (a) analysis:

Step 1: \ce{C6H5NO2 ->[\text{Sn/HCl}] C6H5NH2} (reduction of nitrobenzene → aniline)

Step 2: \ce{C6H5NH2 ->[\text{NaNO}_2/\text{HCl, 0-5°C}] C6H5N2^+Cl^-} (diazotization)

Step 3: \ce{C6H5N2^+Cl^- ->[\beta\text{-naphthol, NaOH}]} azo dye (coupling reaction)

The diazonium salt couples with $\beta$-naphthol in alkaline medium to give an orange-red azo dye ($\ce{-N=N-}$ linkage).

→ Option (a) gives azo dye ✓

Other options involve different reactions (sulfonamide synthesis, nitrile hydrolysis, etc.) and do not produce azo dyes.

Answer: Option (a)

Key Points to Remember:

• Azo dye synthesis: Primary aromatic amine → diazotization (NaNO₂/HCl, 0–5°C) → coupling with phenol/naphthol in alkaline medium
• Coupling reaction: diazonium salt + $\beta$-naphthol → $\ce{-N=N-}$ (azo linkage)
• $\beta$-naphthol + NaOH provides alkaline medium for coupling