The compound with the highest boiling point is

Options

A. n-hexane
B. n-pentane
C. 2,2-dimethylpropane
D. 2-methylbutane.

Answer

To determine which compound has the highest boiling point among n-hexane, n-pentane, 2,2-dimethylpropane, and 2-methylbutane, we need to consider the relationship between boiling point, surface area, and molecular structure.

### Step-by-Step Solution:

1. **Understanding Boiling Point**: The boiling point of a compound is influenced by its molecular structure, specifically its surface area. Generally, larger surface areas lead to higher boiling points because more energy (heat) is required to overcome intermolecular forces.

2. **Analyzing the Given Compounds**:
- **n-Hexane**: This compound has a straight-chain structure with 6 carbon atoms (C6H14). It has a long carbon chain and no branching.
- **n-Pentane**: This compound has a straight-chain structure with 5 carbon atoms (C5H12). It is shorter than n-hexane and has no branching.
- **2,2-Dimethylpropane**: This compound has a branched structure with a total of 5 carbon atoms (C5H12). The main chain is only 3 carbons long, and the branching reduces the surface area.
- **2-Methylbutane**: This compound has a branched structure with a total of 5 carbon atoms (C5H12). The main chain is 4 carbons long, but it also has branching, which reduces the surface area.

3. **Comparing Surface Areas**:
- n-Hexane has the longest carbon chain (6 carbons) and no branching, giving it the largest surface area.
- n-Pentane has a shorter chain (5 carbons) and no branching, so it has a smaller surface area than n-hexane.
- 2,2-Dimethylpropane has a smaller effective chain length due to branching, which decreases its surface area.
- 2-Methylbutane also has branching and a shorter main chain than n-hexane.

4. **Conclusion**: Based on the analysis, n-hexane, with its longer chain and no branching, will have the highest boiling point among the given compounds.

### Final Answer:
The compound with the highest boiling point is **n-hexane**.