Consider the following statements about diazonium salts.
(A) In a diazonium salt RN2+X−, R stands for an aryl group and X− may be Cl−, Br− or BF4−.
(B) Benzenediazonium chloride decomposes easily in the dry state.
(C) In the preparation of benzenediazonium chloride, nitrous acid is produced in the reaction mixture by the reaction of sodium nitrate with hydrochloric acid.
(D) Benzenediazonium chloride is a coloured crystalline solid which is readily soluble in water.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (B) only
Diazonium salts carry the diazonium group, \( \ce{-N2+} \), joined to an aryl group. Benzenediazonium chloride is made from aniline and nitrous acid at 273–278 K; the nitrous acid is formed in the mixture itself from sodium nitrite and hydrochloric acid:
\( \displaystyle \ce{C6H5NH2 + NaNO2 + 2HCl} \xrightarrow{\text{273-278 K}} \ce{C6H5N2^+Cl^- + NaCl + 2H2O} \)
(A) In a diazonium salt RN2+X−, R stands for an aryl group and X− may be Cl−, Br− or BF4−. — True. This is the general formula; the anion may also be \( \ce{HSO4-} \).
(B) Benzenediazonium chloride decomposes easily in the dry state. — True. The salt is stable only in cold solution; as a dry solid it decomposes easily.
(C) In the preparation of benzenediazonium chloride, nitrous acid is produced in the reaction mixture by the reaction of sodium nitrate with hydrochloric acid. — False. Nitrous acid (HNO2) comes from sodium nitrite, NaNO2, not sodium nitrate, NaNO3:
\( \displaystyle \ce{NaNO2 + HCl -> HNO2 + NaCl} \)
(D) Benzenediazonium chloride is a coloured crystalline solid which is readily soluble in water. — False. It is readily soluble in water, but it is a colourless crystalline solid.
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.”
9.7 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.”
9.8 Physical Properties – “Benzenediazonium chloride is a colourless crystalline solid. It is readily soluble in water and is stable in cold but reacts with water when warmed. It decomposes easily in the dry state.”