Which of the following has a lower boiling point than ethanamine?

The correct answer is Option (1) → Propane

• Ethanamine, \( \ce{C2H5NH2} \) (molar mass 45), is a primary amine: its molecules are held together by intermolecular hydrogen bonds (N–H···N).

• Propane, \( \ce{CH3CH2CH3} \) (molar mass 44), is a non-polar alkane with no hydrogen bonding, only weak van der Waals forces, so it boils far lower. Amines boil higher than alkanes of almost the same molar mass.

Why the other options are incorrect

Option (2) Methanoic acid — Incorrect. Carboxylic acids are more extensively hydrogen bonded than alcohols, and alcohols more than amines, so methanoic acid boils higher than ethanamine.

Option (3) Ethanol — Incorrect. O is more electronegative than N, so alcohols are more polar and form stronger hydrogen bonds than amines; ethanol (molar mass 46) boils higher.

Option (4) Propan-1-amine — Incorrect. It is also a primary amine, but with one carbon more: the larger molecule has stronger van der Waals forces and a higher boiling point.

NCERT (2026-27 edition):
9.5 Physical Properties – “Primary and secondary amines are engaged in intermolecular association due to hydrogen bonding between nitrogen of one and hydrogen of another molecule. … Boiling points of amines, alcohols and alkanes of almost the same molar mass are shown in Table 9.2.”

Table 9.2: Comparison of Boiling Points of Amines, Alcohols and Alkanes of Similar Molecular Masses