Assertion: Boiling point of pentane is higher than 2,2-dimethylpropane.
Reason: There is steady increase in boiling point with increase in molecular mass.

Options

A. If both assertion and reson are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the question regarding the boiling points of pentane and 2,2-dimethylpropane, we will break down the assertion and reason step by step.

### Step 1: Understanding the Compounds
- **Assertion**: The assertion states that the boiling point of pentane is higher than that of 2,2-dimethylpropane.
- **Reason**: The reason given is that there is a steady increase in boiling point with an increase in molecular mass.

### Step 2: Analyzing the Structures
- **Pentane**: Pentane (C5H12) is a straight-chain alkane with five carbon atoms.
- **2,2-Dimethylpropane**: 2,2-Dimethylpropane (C5H12) is a branched alkane with the same molecular formula but a different structure, where two methyl groups are attached to the second carbon of propane.

### Step 3: Comparing Surface Areas
- **Surface Area**: The structure of pentane allows for a larger surface area compared to 2,2-dimethylpropane.
- **Effect of Surface Area**: A larger surface area leads to stronger van der Waals forces (intermolecular forces) because there is more area for these forces to act upon.

### Step 4: Understanding Boiling Points
- **Boiling Point**: The boiling point of a substance is influenced by the strength of the intermolecular forces.
- **Van der Waals Forces**: Since pentane has a larger surface area, it experiences stronger van der Waals forces compared to 2,2-dimethylpropane, leading to a higher boiling point for pentane.

### Step 5: Evaluating the Reason
- **Molecular Mass**: While it is true that the boiling point generally increases with molecular mass due to increased van der Waals forces, both pentane and 2,2-dimethylpropane have the same molecular mass.
- **Conclusion on Reason**: The reason provided does not correctly explain why pentane has a higher boiling point than 2,2-dimethylpropane, as the boiling point difference is primarily due to the difference in structure and surface area, not just molecular mass.

### Final Conclusion
- **Assertion**: True (pentane has a higher boiling point than 2,2-dimethylpropane).
- **Reason**: True (boiling points generally increase with molecular mass), but it does not explain the assertion correctly.
- **Correct Answer**: Both the assertion and reason are true, but the reason is not the correct explanation for the assertion.