Assertion : Prolonged intraspecific competition causes an increases in the size of the niche of a population.
Reason : In such a population, use of a new type of resource will increase through the generations.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Prolonged intraspecific competition causes an increase in the size of the niche of a population."
- Intraspecific competition refers to competition among individuals of the same species for limited resources. When this competition is prolonged, individuals may need to adapt to survive.

2. **Understanding the Niche**:
- A niche encompasses both the habitat an organism occupies and its role in the ecosystem, including the resources it utilizes.
- If competition is intense and prolonged, individuals that cannot compete effectively (competitively inferior individuals) will need to find alternative resources or adapt to survive.

3. **Analyzing the Reason**:
- The reason states that "In such a population, use of a new type of resource will increase through the generations."
- This suggests that over time, as individuals adapt to avoid direct competition, they will begin to exploit different resources, thereby expanding the niche.

4. **Connecting Assertion and Reason**:
- The assertion and reason are linked: prolonged intraspecific competition leads to adaptations that allow individuals to utilize new resources, thus increasing the size of the niche.
- Therefore, both the assertion and reason are correct, and the reason accurately explains the assertion.

5. **Conclusion**:
- Based on the analysis, the correct answer is that both the assertion and reason are correct, and the reason correctly explains the assertion.

### Final Answer:
**Both assertion and reason are correct, and the reason is correctly explaining the assertion.**

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