Arrange the following sets of compounds in order of their increasing boiling points:
(A) Pentanol
(B) Butanol
(C) Ethanol
(D) Propanol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C), (D), (B), (A)
All alcohols have high boiling points because their molecules are joined by intermolecular hydrogen bonds. In a homologous series of alcohols, every molecule has one –OH group, so the hydrogen bonding is similar. The difference comes from the van der Waals forces, which grow with the size and surface area of the molecule. So the boiling point increases with the number of carbon atoms.
\( \displaystyle \text{Ethanol (C}_2) < \text{Propanol (C}_3) < \text{Butanol (C}_4) < \text{Pentanol (C}_5) \)
\( \displaystyle 351\ \mathrm{K} < 370\ \mathrm{K} < 391\ \mathrm{K} < 411\ \mathrm{K} \)
Matching the labels:
(C) Ethanol: 2 carbon atoms
(D) Propanol: 3 carbon atoms
(B) Butanol: 4 carbon atoms
(A) Pentanol: 5 carbon atoms
NCERT (2026-27 edition):
Boiling Points
