Primary, secondary and tertiary amines differ from one another in many of their reactions. Which of the following decides the course of these reactions?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → The number of hydrogen atoms attached to the nitrogen atom
A primary amine has the group –NH2, a secondary amine >N–H and a tertiary amine >N– with no hydrogen. Many reactions of amines replace or use these N–H hydrogens, so the three classes react differently. This is also why such reactions are used to tell primary, secondary and tertiary amines apart.
Why the other options are incorrect
Option (1) The number of carbon atoms in the alkyl groups — Incorrect. Ethanamine and butan-1-amine have different numbers of carbon atoms, yet both are primary amines and react in the same way.
Option (2) The hybridisation of the nitrogen atom — Incorrect. Nitrogen is sp3 hybridised in all amines, so it cannot make the three classes differ.
Option (3) The molar mass of the amine — Incorrect. Isomeric amines such as butan-1-amine and N,N-dimethylethanamine have the same molar mass but belong to different classes and react differently.
NCERT (2026-27 edition):
9.6 Chemical Reactions – “…The number of hydrogen atoms attached to nitrogen atom also decides the course of reaction of amines; that is why primary (–NH2), secondary (>N–H) and tertiary amines (>N–) differ in many reactions.”