Which of the following has the highest boiling point?

The correct answer is Option (4) → Hexanol

Alcohols are associated by hydrogen bonding; among them the boiling point rises with the number of carbon atoms and falls with branching.

Taking pentanol and hexanol as the straight-chain alcohols with OH on C-1, the boiling points are:

    2-methylpropan-1-ol (\( \ce{C4} \)): 381 K
    pentan-2-ol (\( \ce{C5} \)): 392 K
    pentan-1-ol (\( \ce{C5} \)): 411 K
    hexan-1-ol (\( \ce{C6} \)): 430 K

So hexanol, with the most carbon atoms, has the highest boiling point.

Shortcut: Hexanol is the only alcohol with six carbon atoms, so it boils highest without comparing branching.

Why the other options are incorrect

• Option (1) 2-methylpropanol — Incorrect. It has only four carbon atoms and a branched chain, so it boils lowest of the four.

• Option (2) Pentan-2-ol — Incorrect. It has five carbon atoms, and with OH on C-2 it is more branched than pentan-1-ol, so it boils lower.

• Option (3) Pentanol — Incorrect. The straight five-carbon chain gives it a higher boiling point than its branched isomer, but it still has one carbon atom fewer than hexanol.

NCERT (2026-27 edition):
Physical Properties – …