Read the passage carefully and answer the Questions.

Amines are classified as primary (1°), secondary (2°) and tertiary (3°) depending upon the number of hydrogen atoms replaced by alkyl or aryl groups in ammonia molecules. Aliphatic amines are a stronger bases due to +1 effect of an alkyl groups. Intermolecular hydrogen bonding in primary and secondary amines affects the boiling points of amines. The intermolecular association is more in primary amines than in secondary amines as there are more number of hydrogen atoms available for hydrogen bond formation. Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum and also by reduction with metals in an acidic medium. Gabriel synthesis is used for the preparation of primary amines. Primary amines react with nitrous acid to give unstable diazonium-salts which can be used to synthesize a variety of compounds.

The compound having the highest boiling point is

n-Butanol

The correct answer is Option (3) → n-Butanol.

Statement: Among the given compounds, n-Butanol has the highest boiling point.
Reason: Boiling point depends mainly on the strength of intermolecular forces, especially hydrogen bonding.

Comparison

• n-Pentane

• Non-polar hydrocarbon

• Only London dispersion forces

• Lowest boiling point

• Diethylamine (secondary amine)

• Has one N–H bond → limited hydrogen bonding

• Weaker than alcohol hydrogen bonding

• n-Butylamine (primary amine)

• Has two N–H bonds → more hydrogen bonding than secondary amine

• But N–H hydrogen bonding is weaker than O–H

• n-Butanol (alcohol)

• Contains O–H group

• Oxygen is more electronegative than nitrogen

• Forms strongest intermolecular hydrogen bonding network

Key idea:
Strength of H-bonding:
O–H (alcohol) > N–H (amines) > no H-bond (alkane)

Conclusion:
Because n-Butanol forms the strongest intermolecular hydrogen bonding, it has the highest boiling point among the given compounds.

$\text{Order: n-Pentane < Diethylamine < n-Butylamine < n-Butanol}$