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). | 
