Which of the following reagents will bring out the following transfor…

The correct answer is Option (1) → (A) and (C) only

Replacing –\( \ce{NH2} \) on a benzene ring by –Cl takes two steps.

1. Diazotisation. A primary aromatic amine reacts with nitrous acid at 273–278 K to give a diazonium salt. Nitrous acid is unstable, so it is made in the mixture itself from NaNO₂ and HCl. In NaOH no nitrous acid can form, so no diazonium salt is obtained.

    \( \displaystyle \ce{C6H5NH2 + NaNO2 + 2HCl} \xrightarrow{\text{273-278 K}} \ce{C6H5N2^+Cl^- + NaCl + 2H2O} \)

2. Replacement of the diazonium group by Cl. This can be done in two ways:

• Sandmeyer reaction: \( \ce{Cu2Cl2} \)/HCl

      \( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu2Cl2/HCl}} \ce{C6H5Cl + N2} \)

• Gattermann reaction: copper powder with HCl

      \( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu/HCl}} \ce{C6H5Cl + N2} \)

Judging each set of reagents:

• (A) NaNO₂/HCl and Cu/HCl — Correct. Diazotisation followed by the Gattermann reaction.

• (B) NaNO₂/NaOH and Cu/HCl — Incorrect. \( \ce{NaNO2} \) in NaOH gives no nitrous acid, so the diazonium salt is never formed.

• (C) NaNO₂/HCl and Cu₂Cl₂/HCl — Correct. Diazotisation followed by the Sandmeyer reaction.

• (D) NaNO₂/NaOH and Cu₂Cl₂/HCl — Incorrect. The first step fails for the same reason as in (B).

NCERT (2026-27 edition):
Method of Preparation of Diazonium Salts – “Benzenediazonium chloride is prepared by the reaction of aniline with nitrous acid at 273-278K. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The conversion of primary aromatic amines into diazonium salts is known as diazotisation.”

Replacement by Halide or Cyanide Ion