What is the reason for the stability of aromatic diazonium salts?

The correct answer is Option (2) → Dispersal of positive charge over benzene ring

• A diazonium salt has the formula \( \ce{R-N2^+X^-} \); the diazonium group \( \ce{-N2^+} \) carries a positive charge. In an arenediazonium ion this group is joined to a benzene ring, and resonance with the ring spreads the positive charge over the benzene ring.

• Spreading the charge over several atoms lowers the energy of the ion, so arenediazonium salts are stable for a short time in cold solution (273–278 K). An alkyl group cannot delocalise the charge, so alkyldiazonium salts are highly unstable and lose \( \ce{N2} \) at once. The stability “explained on the basis of resonance” is this dispersal of positive charge.

Why the other options are incorrect

Option (1) Dispersal of negative charge over the benzene ring — Incorrect. The diazonium ion is a cation; the charge spread over the ring by resonance is positive, not negative.

Option (3) Bond between diazonium group and anion — Incorrect. The diazonium cation and \( \ce{X^-} \) are held by ionic attraction, which is present in the unstable alkyldiazonium salts too, so it cannot explain the extra stability of the aryl salts.

Option (4) High electronegativity of anion compared to the N atom — Incorrect. The anion (\( \ce{Cl^-} \), \( \ce{HSO4^-} \), \( \ce{BF4^-} \)) does not delocalise the charge of the cation. Alkyl and aryl diazonium chlorides have the same anion but very different stability.

NCERT (2026-27 edition):
II. DIAZONIUM SALTS – “The diazonium salts have the general formula R N₂⁺ X^– where R stands for an aryl group and X^– ion may be Cl^–, Br^–, HSO₄^–, BF₄^–, etc. … The N₂⁺ group is called diazonium group.”
“… Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273-278 K). The stability of arenediazonium ion is explained on the basis of resonance.”