Assertion: Natality potential is never realised.
Reason: Biotic potential is countered by environmental resistance

Options

A. (a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. (b) If both Assertion and Reason are true and the Reason is not the correct explanation of the Assertion.
C. (c) If Assertion is true but the Reason is false
D. (d) If both Assertion and Reason are false.

Explanation

To solve the assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Natality potential is never realized."
- Natality potential refers to the maximum reproductive capacity of an organism under ideal conditions. It implies that organisms have the potential to reproduce at a certain rate, but this potential is not fully achieved in natural settings.

2. **Understanding the Reason**:
- The reason states that "Biotic potential is countered by environmental resistance."
- Biotic potential is the maximum capacity of an organism to reproduce under optimal environmental conditions. Environmental resistance includes factors that limit population growth, such as food scarcity, predation, disease, and competition.

3. **Connecting the Assertion and Reason**:
- The assertion is true because, in natural environments, organisms do not reach their maximum natality potential due to various limiting factors.
- The reason is also true as environmental resistance indeed counteracts the biotic potential, preventing populations from growing indefinitely.

4. **Conclusion**:
- Since both the assertion and the reason are true, and the reason provides a correct explanation for the assertion, we conclude that the correct answer is option A: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
- **Option A**: Both assertion and reason are true, and the reason is the correct explanation of the assertion.