Assertion : The method of development of embryo sac from a single functional megaspore is termed as monosporic development.
Reason : In monosporic (Polygonum) type of embryo sac development, usually the megaspore which is situated towards micropylar end remains functional.

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

To analyze the given assertion and reason, we can break down the information step by step:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the development of the embryo sac from a single functional megaspore is termed as monosporic development.
- This is a true statement because monosporic development refers specifically to the formation of the embryo sac from one functional megaspore.

2. **Understanding the Reason**:
- The reason provided explains that in the monosporic (Polygonum) type of embryo sac development, the megaspore located at the micropylar end remains functional.
- This statement is also true, as in the Polygonum type, it is indeed the megaspore at the micropylar end that develops into the embryo sac while the other three megaspores degenerate.

3. **Evaluating the Relationship**:
- While both the assertion and reason are true, we need to determine if the reason correctly explains the assertion.
- The assertion describes what monosporic development is, while the reason gives a specific example of how it occurs in Polygonum. However, the reason does not directly explain why the method of development is termed "monosporic."

4. **Conclusion**:
- Since both the assertion and reason are true, but the reason does not serve as a correct explanation for the assertion, the correct option is that both are true but the reason is not the correct explanation of the assertion.

### Final Answer:
The correct option is **2. If both assertion and reason are true but the reason is not the correct explanation of the assertion.**