Which one of the following gives onlyh one monochloro derivative?

Options

A. neo-Pentane
B. n-Hexane
C. 2-ethylpentane
D. 3-Methylpentane

Explanation

To determine which compound gives only one monochloro derivative, we need to analyze the structures of the given options and the types of hydrogen atoms present in each compound.

### Step-by-step Solution:

1. **Identify the Compounds**: The question provides four options:
- A) Neopentane
- B) n-Hexane
- C) 2-Ethylpentane
- D) 3-Methylpentane

2. **Analyze Neopentane**:
- Neopentane has the structure:
\[ \text{(CH}_3\text{)}_4\text{C} \]
- In this structure, all the hydrogen atoms are attached to primary (1°) carbon atoms.
- Since there is only one type of hydrogen (1° hydrogen), neopentane can only form one monochloro derivative when one hydrogen is replaced by chlorine.

3. **Analyze n-Hexane**:
- n-Hexane has the structure:
\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3 \]
- This compound contains both primary (1°) and secondary (2°) hydrogen atoms.
- Therefore, it can form multiple monochloro derivatives, not just one.

4. **Analyze 2-Ethylpentane**:
- 2-Ethylpentane has the structure:
\[ \text{CH}_3\text{CH}(\text{C}_2\text{H}_5)\text{CH}_2\text{CH}_3 \]
- This compound contains primary (1°), secondary (2°), and tertiary (3°) hydrogen atoms.
- Thus, it can also form multiple monochloro derivatives.

5. **Analyze 3-Methylpentane**:
- 3-Methylpentane has the structure:
\[ \text{CH}_3\text{CH}_2\text{C}(\text{CH}_3)\text{CH}_2\text{CH}_3 \]
- Similar to 2-Ethylpentane, this compound contains primary (1°), secondary (2°), and tertiary (3°) hydrogen atoms.
- Therefore, it can form multiple monochloro derivatives as well.

6. **Conclusion**:
- Among the options analyzed, only **neopentane** gives **one monochloro derivative** because it has only primary hydrogen atoms.
- Therefore, **the correct answer is A) Neopentane**.