Answer the question on the basis of passage given below:
There are three kinds of amines which are primary, secondary and tertiary amines. These amines may have alkyl group or aryl group or both alkyl and aryl groups. These amines can be distinguished from one another by various chemical tests.
An amine \(A\) on treatment with \(NaNO_2\) and \(HCl\) at \(273-277 K\), followed by treatment with ethyl alcohol gives a compound \(B\) with an empirical formula of \(CH\) and molecular mass \(78\), \(A\) is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → aniline (C6H5NH2)
Only primary aromatic amines give stable diazonium salts with \( \ce{NaNO2} \) and HCl at 273-277 K (diazotisation). The diazo group can then be replaced by hydrogen with mild reducing agents such as ethanol (or hypophosphorous acid).
Compound B has empirical formula CH (empirical mass 13) and molecular mass 78, so its molecular formula is \( \ce{(CH)6} \) = \( \ce{C6H6} \), benzene. Working back, the diazonium salt was benzenediazonium chloride and A is aniline:
\( \ce{C6H5NH2 + NaNO2 + 2HCl} \xrightarrow{\ce{273-277 K}} \ce{C6H5N2+Cl- + NaCl + 2H2O} \)
\( \ce{C6H5N2+Cl- + CH3CH2OH -> C6H6 + N2 + CH3CHO + HCl} \)
Why the other options are incorrect
Option (1) C6H13N — Incorrect. A saturated amine (such as cyclohexylamine); its aliphatic diazonium salt decomposes to an alcohol and \( \ce{N2} \), not to \( \ce{C6H6} \).
Option (3) CH3(CH2)5NH2 — Incorrect. Hexylamine is a primary aliphatic amine; with nitrous acid it gives hexan-1-ol (and other products) with \( \ce{N2} \), not benzene.
Option (4) benzylamine (C6H5CH2NH2) — Incorrect. The –\( \ce{NH2} \) is on an alkyl carbon, so it behaves as an aliphatic amine and gives benzyl alcohol and \( \ce{N2} \).
NCERT (2026-27 edition):
Chemical Reactions – …
