Identify the most volatile compound

The correct answer is Option (4) → Propane

Reason (Boiling Point Comparison):

Compound	Type	Approx. Boiling Point (°C)	Volatility Order
1. n-Butanol	Primary alcohol (C4)	+117	Least volatile
2. Triethylamine	Tertiary amine (C6)	+89	↓
3. Propylamine	Primary amine (C3)	+48	↓
4. Propane	Alkane (C3)	–42	Most volatile

Key Points:

• Alcohols have strong H-bonding → very high BP
• Primary amines have H-bonding → moderate BP
• Tertiary amines have no H-bonding → lower BP than primary amines of similar mass
• Alkanes have only weak van der Waals forces → very low BP

So, propane (a small non-polar molecule) is by far the most volatile (lowest boiling point, easily gaseous at room temperature).