Assertion : At zero degree kelvin, the volume occupied by a gas is negligible.
Reason : All molecular motion ceases at `0 K`.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion
B. If both assertion and reason are correct and reason is not correct explanation for assertion
C. If assertion is correct but reason is incorrect
D. If assertion and reason are both incorreect.

Explanation

To analyze the given assertion and reason, we will break it down step by step.

### Step 1: Understanding the Assertion
The assertion states that "At zero degree Kelvin, the volume occupied by a gas is negligible."

**Explanation:**
- According to Charles's Law, the volume of a gas is directly proportional to its temperature (in Kelvin). As the temperature approaches absolute zero (0 K), the volume of the gas approaches zero.
- Therefore, the assertion is true: at 0 K, the volume occupied by a gas is indeed negligible.

### Step 2: Understanding the Reason
The reason states that "All molecular motion ceases at 0 K."

**Explanation:**
- At absolute zero (0 K), it is often said that molecular motion stops. However, this is not entirely accurate. While translational motion (the movement of molecules through space) does cease, quantum mechanics tells us that molecules still possess zero-point energy, which means that some vibrational motion can still occur.
- Therefore, the reason is false: not all molecular motion ceases at 0 K.

### Step 3: Conclusion
Based on the analysis:
- The assertion is true.
- The reason is false.

Thus, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
Assertion: True
Reason: False
Therefore, the answer is option C.

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