The correct answer is Option (2) → Gatterman reaction
When benzene diazonium chloride is treated with halogen acid in the presence of copper powder, the reaction is called the Gattermann Reaction.
Reasoning with all options:
Option (1) – Finkelstein Reaction
This reaction is used to convert alkyl chlorides or bromides into alkyl iodides using sodium iodide in acetone.
It does not involve diazonium salts. Therefore, it is incorrect.
Option (2) – Gattermann Reaction
In this reaction, the diazonium group (–N₂⁺) is replaced by Cl or Br using HCl or HBr and copper powder.
This exactly matches the condition given in the question. Therefore, it is correct.
Option (3) – Sandmeyer Reaction
This reaction is also related to diazonium salts, but it uses copper salts like CuCl or CuBr, not copper powder and halogen acid.
Hence, it does not match the question.
Option (4) – Hell–Volhard–Zelinsky Reaction
This reaction is used for alpha-halogenation of carboxylic acids using halogen and red phosphorus.
It is completely different from diazonium salt reactions. Therefore, it is incorrect.
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