Assertion: Archaebacteria are most resistant to adverse environmental conditions.
Reason: In archaebacteria, cell wall and cell membrane are highly complex.

Options

A. If both assertion and Reason are true and the reason is a correct explanation of the assertion.
B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion and Reason are False.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Archaebacteria are most resistant to adverse environmental conditions." This indicates that archaebacteria can survive in extreme environments such as hot springs, salt lakes, and acidic waters.

2. **Understanding the Reason**: The reason provided is that "In archaebacteria, cell wall and cell membrane are highly complex." This suggests that the structural complexity of their cell wall and membrane contributes to their resilience in harsh conditions.

3. **Analyzing the Assertion**: Archaebacteria are indeed known for their ability to thrive in extreme environments, which supports the assertion. They have unique adaptations that allow them to survive where most other organisms cannot.

4. **Analyzing the Reason**: The complexity of the cell wall and cell membrane in archaebacteria is a significant factor in their ability to withstand extreme conditions. Their cell walls are composed of unique molecules (like pseudopeptidoglycan) that provide stability and protection.

5. **Conclusion**: Both the assertion and the reason are true. The reason provided accurately explains why archaebacteria are resistant to adverse environmental conditions.

6. **Final Answer**: Therefore, the correct answer is that both the assertion and the reason are true, and the reason is the correct explanation of the assertion.