Assertion : Intercropping checks the population of insects.
Reason : Plant pests can be controlled biologically by their natural parasites and pathogens.

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that intercropping checks the population of insects. Intercropping is a method where two or more crops are grown together in the same field. This technique can help reduce the population of certain pests.

2. **Explaining Intercropping**:
- In intercropping, different crops are planted together, which can lead to a diverse ecosystem. For example, if crop A is affected by a specific pest, and crop B is not, the presence of crop B can help protect crop A from being entirely destroyed by that pest. This diversity can disrupt the life cycles of pests, thereby controlling their population.

3. **Understanding the Reason**:
- The reason provided states that plant pests can be controlled biologically by their natural parasites and pathogens. This means that there are organisms in nature that can help control pest populations by preying on them or causing diseases.

4. **Analyzing the Relationship**:
- While both the assertion and the reason are true, they are not directly related. Intercropping controls pest populations through crop diversity, while the reason discusses biological control through natural enemies of pests. Therefore, the assertion is correct, and the reason is also correct, but the reason does not explain the assertion.

5. **Conclusion**:
- The final conclusion is that both the assertion and the reason are correct, but the reason is not the correct explanation for the assertion.

### Final Answer:
- **Assertion**: True
- **Reason**: True
- **Relationship**: The reason is not the correct explanation for the assertion.