An alkane forms isomers if the number of least carbon atom is

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To determine the minimum number of carbon atoms required for an alkane to form isomers, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Isomerism**: Isomerism occurs when two or more compounds have the same molecular formula but different structural arrangements. For alkanes, this means that as the number of carbon atoms increases, the potential for different structural arrangements (isomers) also increases.

2. **Identifying the General Formula**: The general formula for alkanes is CnH2n+2, where 'n' is the number of carbon atoms.

3. **Analyzing Small Alkanes**:
- For **n = 1** (C1H4): The only compound is methane (CH4). There are no isomers.
- For **n = 2** (C2H6): The only compound is ethane (C2H6). There are no isomers.
- For **n = 3** (C3H8): The only compound is propane (C3H8). There are no isomers.
- For **n = 4** (C4H10): The compounds are butane (C4H10) and isobutane (C4H10). Here, we have two isomers.

4. **Conclusion**: The minimum number of carbon atoms required for an alkane to exhibit isomerism is **4**.

Thus, the answer is that an alkane forms isomers if the number of least carbon atoms is **4**.