Assertion : When hot water is poured in a beaker of thick glass, the beaker cracks.
Reason : Outer surface of the beaker expands suddenly.

Options

A. If both assertion and reason 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 solve the question, we need to analyze the assertion and reason provided:

**Assertion:** When hot water is poured into a beaker of thick glass, the beaker cracks.

**Reason:** The outer surface of the beaker expands suddenly.

### Step-by-Step Solution:

1. **Understanding the Assertion:**
- When hot water is poured into a thick glass beaker, the temperature difference between the hot water and the glass causes stress within the material of the glass. The inner surface of the glass heats up quickly, while the outer surface remains relatively cooler.

2. **Thermal Expansion:**
- Glass, like most materials, expands when heated. However, the expansion is not uniform in this case. The inner surface of the beaker, which is in contact with the hot water, expands rapidly, while the outer surface does not heat up as quickly. This creates a situation where the inner part of the glass is trying to expand more than the outer part.

3. **Stress and Cracking:**
- This differential expansion leads to stress within the glass. If the stress exceeds the strength of the glass, it results in cracking. Therefore, the assertion that the beaker cracks is true.

4. **Evaluating the Reason:**
- The reason states that the outer surface of the beaker expands suddenly. However, this is not accurate. The outer surface does not expand suddenly; it remains at a relatively constant temperature for a longer time compared to the inner surface. The cracking occurs due to the rapid expansion of the inner surface and the slower expansion of the outer surface, leading to stress.

5. **Conclusion:**
- The assertion is true, but the reason provided is false. Therefore, the correct option is that the assertion is true, but the reason is false.

### Final Answer:
The correct option is C: Assertion is true, but the reason is false.