Assertion: The heat absorbed during the isothermal expansion of an ideal gas against vacuum is zero.
Reason: The volume occupied by the molecules of an ideal gas is zero.

Options

A. If both (`A`) and (`R`) are correct and (`R`) is the correct explanation of (`A`).
B. If both (`A`) and (`R`) are correct, but (`R`) is not the correct explanation of (`A`).
C. If (`A`) is correct, but (`R`) is incorrect.
D. If (`A`) is incorrect, but (`R`) is correct.

Explanation

To solve the assertion and reason question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states that "The heat absorbed during the isothermal expansion of an ideal gas against vacuum is zero."

- **Isothermal Expansion**: This refers to a process where the temperature of the gas remains constant.
- **Against Vacuum**: When an ideal gas expands against a vacuum, there are no external pressures to work against.
- **Heat Absorption**: For an ideal gas expanding against a vacuum, there are no intermolecular forces to overcome, and therefore, no heat is required from the surroundings to facilitate the expansion.

**Conclusion for Assertion**: The assertion is correct because, in the case of an ideal gas expanding against a vacuum, no heat is absorbed.

### Step 2: Analyze the Reason
The reason states that "The volume occupied by the molecules of an ideal gas is zero."

- **Volume of Ideal Gas Molecules**: In the ideal gas model, it is assumed that the volume occupied by the gas molecules themselves is negligible compared to the volume of the container.
- **Relevance to Assertion**: While this statement is true, it does not explain why no heat is absorbed during the expansion. The lack of intermolecular forces is the key factor in explaining the assertion.

**Conclusion for Reason**: The reason is correct but does not provide a valid explanation for the assertion.

### Step 3: Determine the Relationship
Based on the analysis:
- The assertion is true.
- The reason is true but does not explain the assertion.

Thus, the correct answer is that both the assertion and reason are correct, but the reason is not the correct explanation for the assertion.

### Final Answer
The correct answer is: **B** - Both A and R are correct, but R is not the correct explanation for A.

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