Assertion
In imbricate aestivation, out of five petals, one is completely internal, one is completely external and in each of the remaining three petals, one margin is internal and the other is external.

Reason
Ascending imbricate aestivation is found in Cassia and Gulmohur.

A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

C) Assertion is correct but Reason is incorrect

D) Both Assertion and Reason are incorrect

To address your question, let's break down the concepts of imbricate aestivation and the specific examples provided. Aestivation refers to the arrangement of petals in a flower bud before it opens, and imbricate is a specific type of aestivation where the petals overlap each other. The assertion states that in imbricate aestivation, one petal is completely internal, one is completely external, and the remaining three petals have one margin internal and the other external. The reason given is that ascending imbricate aestivation is found in plants like Cassia and Gulmohur.

Analyzing the Assertion

The assertion describes a specific arrangement of petals in imbricate aestivation. In this type, it is indeed true that petals can overlap in such a way that some are completely internal while others are external. However, the description of the arrangement with three petals having one margin internal and the other external is somewhat misleading. Typically, in true imbricate aestivation, the petals overlap in a more complex manner, and the arrangement can vary significantly among different species.

Evaluating the Reason

Now, let's consider the reason provided. Ascending imbricate aestivation is indeed observed in plants like Cassia and Gulmohur. This means that the petals do overlap, but the specific arrangement can differ. The reason is correct in identifying the plants that exhibit this type of aestivation, but it does not accurately explain the assertion about the specific arrangement of petals.

Conclusion on the Options

• A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C) Assertion is correct but Reason is incorrect
• D) Both Assertion and Reason are incorrect

Given this analysis, the best choice is B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion. The assertion does describe a type of aestivation, but the specifics are not entirely accurate, and while the reason correctly identifies examples of ascending imbricate aestivation, it does not clarify the assertion's details.