The product A formed in the following reaction is

 A

CONCEPT:

Diazotization Reaction

• Diazotization is the process of forming a diazonium salt (ArN₂Cl) from an amine group (-NH₂) in an aromatic compound by reaction with nitrous acid (HNO₂) generated in situ.
• The general reaction for diazotization is:

  Ar-NH₂ + HNO₂ → Ar-N₂Cl

  where Ar is an aromatic ring.
• In this process, the amino group (-NH₂) on the aromatic ring is converted into a diazonium group (Ar-N₂Cl), which is a highly reactive intermediate that can undergo further reactions, such as substitution with various nucleophiles.
• The diazonium group (Ar-N₂Cl) is often used to introduce a halogen (e.g., chlorine) onto the aromatic ring by subsequent treatment with a halogenating agent like Cl_2.

EXPLANATION:

• In the given reaction:

  The starting compound is aniline (C₆H₅NH₂), which undergoes diazotization with sodium nitrite (NaNO₂) and hydrochloric acid (HCl) at 0°C to form a diazonium salt (C₆H₅–N₂Cl).

  • Here, the amine group (-NH₂) on the benzene ring is converted into a diazonium ion (Ar-N₂Cl).
  • Diazonium ion formation is followed by chlorination with Cl₂ to replace the diazonium group with a chlorine atom (Cl).
• After treatment with Cl₂, the product A is obtained, which is chlorobenzene (C₆H₅Cl).

Therefore, the major product 'A' formed in the reaction is chlorobenzene (C₆H₅Cl).