Assertion (A) : Among isomeric pentanes, 2, 2- dimethylpentane has highest boiling point.
Reason (R) : Branching does not affect the boiling point.

Options

A. Both A and R are correct and R is the correct explanation of A.
B. Both A and R are correct but R is not the correct explanation of A.
C. Both A and R are not correct.
D. A is not correct but R is correct.

Answer

To solve the question, we need to analyze the assertion and reason provided regarding the boiling points of isomeric pentanes, particularly focusing on 2,2-dimethylpentane.

### Step-by-Step Solution:

1. **Identify the Isomers of Pentane**:
- The molecular formula for pentane is C5H12. There are three main structural isomers of pentane:
- **n-Pentane**: CH3-CH2-CH2-CH2-CH3
- **Isopentane (2-methylbutane)**: CH3-CH(CH3)-CH2-CH3
- **Neopentane (2,2-dimethylpropane)**: C(CH3)4 (or 2,2-dimethylpentane)

2. **Understand the Structure of 2,2-Dimethylpentane**:
- 2,2-Dimethylpentane has the structure where two methyl groups are attached to the second carbon of a five-carbon chain. Its structure can be represented as:
- CH3-C(CH3)2-CH2-CH3

3. **Analyze the Effect of Branching on Boiling Point**:
- In hydrocarbons, the boiling point is influenced by the molecular surface area and the degree of branching.
- More branching typically leads to a lower boiling point because it reduces the surface area available for intermolecular interactions (van der Waals forces).

4. **Compare the Boiling Points**:
- Among the isomers:
- **n-Pentane** has the highest boiling point due to its straight-chain structure, which maximizes surface area.
- **Isopentane** has a lower boiling point than n-pentane but higher than 2,2-dimethylpentane.
- **2,2-Dimethylpentane** has the lowest boiling point due to its highly branched structure, which minimizes surface area.

5. **Evaluate the Assertion and Reason**:
- **Assertion (A)**: "Among isomeric pentanes, 2,2-dimethylpentane has the highest boiling point." This is **false**.
- **Reason (R)**: "Branching does not affect the boiling point." This is also **false** because increased branching generally decreases the boiling point.

6. **Conclusion**:
- Both the assertion and the reason are incorrect. Therefore, the correct answer is that both A and R are not correct.

### Final Answer:
Both Assertion (A) and Reason (R) are incorrect.