Arrange the following compounds according to increasing order of...

Boiling point depends on the strength of intermolecular forces.

$n\text{-C}_4\text{H}_{10}$ (C) is a nonpolar alkane with only weak van der Waals forces, resulting in the lowest boiling point.

$n\text{-C}_4\text{H}_9\text{OH}$ (A) is an alcohol that forms strong intermolecular hydrogen bonds due to the high electronegativity of oxygen, giving it the highest boiling point.

Both $n\text{-C}_4\text{H}_9\text{NH}_2$ (B)$and \text{C}_2\text{H}_5\text{NHC}_2\text{H}_5$ (D) are amines and form hydrogen bonds, which are weaker than those in alcohols because nitrogen is less electronegative than oxygen.

Between the primary amine (B) and the secondary amine (D), the primary amine has two $\text{N-H}$ bonds available for hydrogen bonding and less steric hindrance, leading to stronger intermolecular forces and a higher boiling point than the secondary amine.

The increasing order of boiling points is $C < D < B < A$.

Answer: $C < D < B < A$