Which one of the following has the lowest boiling point?

Options

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

Explanation

To determine which compound has the lowest boiling point among the given options, we will analyze the structures and branching of each compound.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- 2-Methylbutane
- 2-Methylpropane
- 2,2-Dimethylpropane
- n-Pentane

2. **Understand the Structure**:
- **2-Methylbutane**: This compound has a straight-chain butane with one methyl group on the second carbon.
- **2-Methylpropane**: This compound has three carbons in a chain with one methyl group on the second carbon.
- **2,2-Dimethylpropane**: This compound has a propane chain with two methyl groups attached to the second carbon.
- **n-Pentane**: This is a straight-chain alkane with five carbon atoms.

3. **Consider the Effect of Branching**:
- Generally, the boiling point of alkanes decreases with increased branching. This is because branching reduces the surface area available for intermolecular interactions, leading to lower boiling points.

4. **Count the Carbon Atoms**:
- 2-Methylbutane: 5 carbons
- 2-Methylpropane: 5 carbons
- 2,2-Dimethylpropane: 5 carbons
- n-Pentane: 5 carbons

5. **Analyze the Boiling Points**:
- All compounds have the same number of carbon atoms, but their structures differ in branching.
- Among these, 2,2-Dimethylpropane is the most branched, followed by 2-Methylbutane, then 2-Methylpropane, and finally n-Pentane, which is unbranched.

6. **Determine the Lowest Boiling Point**:
- Since 2-Methylpropane has the least branching among the listed compounds, it will have the lowest boiling point compared to the others.

### Conclusion:
The compound with the lowest boiling point among the options is **2-Methylpropane**.