Which of the following alkanes has the lowest boiling ?

Options

A. n-Pentane
B. Isopentane
C. Neopentano
D. n-Hexane.

Explanation

To determine which alkane has the lowest boiling point among the given options (n-pentane, isopentane, neopentane, and n-hexane), we can follow these steps:

### Step 1: Understand the Factors Affecting Boiling Point
The boiling point of alkanes is influenced by two main factors:
1. **Number of Carbon Atoms**: Generally, as the number of carbon atoms in a straight-chain alkane increases, the boiling point increases due to greater van der Waals forces (intermolecular forces).
2. **Branching**: Increased branching in alkanes decreases the boiling point because it reduces the surface area available for van der Waals interactions.

### Step 2: Analyze the Given Alkanes
We have the following alkanes to consider:
- **n-Pentane** (C5H12): A straight-chain alkane with 5 carbon atoms.
- **Isopentane** (C5H12): A branched alkane with 5 carbon atoms.
- **Neopentane** (C5H12): A more highly branched alkane with 5 carbon atoms.
- **n-Hexane** (C6H14): A straight-chain alkane with 6 carbon atoms.

### Step 3: Compare the Structures
1. **n-Pentane**:
- Structure: CH3-CH2-CH2-CH2-CH3
- Boiling Point: Higher due to its straight-chain structure.

2. **Isopentane**:
- Structure: (CH3)2CH-CH2-CH3
- Boiling Point: Lower than n-pentane due to some branching.

3. **Neopentane**:
- Structure: (CH3)4C
- Boiling Point: Lowest among the three due to increased branching.

4. **n-Hexane**:
- Structure: CH3-CH2-CH2-CH2-CH2-CH3
- Boiling Point: Highest due to having 6 carbon atoms.

### Step 4: Determine the Lowest Boiling Point
From the analysis:
- n-Hexane has the highest boiling point due to having the longest chain.
- n-Pentane has a higher boiling point than isopentane and neopentane.
- Isopentane has a higher boiling point than neopentane.
- Neopentane has the lowest boiling point due to its highly branched structure.

### Conclusion
The alkane with the lowest boiling point among the given options is **neopentane**.

### Final Answer
**Neopentane (Option 3)** has the lowest boiling point.

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