Assertion : When electron and holes combine then this reaction is exothermic .
Reason : Hole electron can not combine.

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that when electrons and holes combine, the reaction is exothermic.
- An exothermic reaction is one that releases energy, typically in the form of heat.

2. **Analyzing Electron-Hole Combination**:
- In semiconductor physics, an electron (which carries a negative charge) can combine with a hole (which can be thought of as a positive charge due to the absence of an electron).
- When an electron fills a hole, it results in the release of energy, as the system moves to a lower energy state.

3. **Conclusion on Assertion**:
- Since the combination of electrons and holes releases energy, the assertion is **true**.

4. **Understanding the Reason**:
- The reason states that holes and electrons cannot combine.
- This statement is incorrect because electrons can indeed combine with holes to form a neutral state.

5. **Conclusion on Reason**:
- Since holes and electrons can combine, the reason is **false**.

6. **Final Evaluation**:
- The assertion is true, and the reason is false. Therefore, the correct conclusion is that the assertion is true, but the reason is false.

### Final Answer:
- **Assertion**: True
- **Reason**: False