Assertion :- Most zygotes divide only after certain amount of endosperm is formed.
Reason :- This is an adaptation to provide assured nutrition to the developing embryo.

Options

A. A
B. B
C. C
D. D

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Most zygotes divide only after a certain amount of endosperm is formed." This implies that the division of zygotes is dependent on the formation of endosperm.

2. **Defining Endosperm**: Endosperm is a tissue that provides nutrition to the developing embryo in angiosperms (flowering plants). It is formed through a process called triple fusion, where one male gamete fuses with two polar nuclei in the embryo sac.

3. **Role of Endosperm**: The endosperm serves as a source of nourishment for the developing embryo. It is rich in reserve food materials that are essential for the growth and development of the embryo.

4. **Analyzing the Reason**: The reason states that "This is an adaptation to provide assured nutrition to the developing embryo." This suggests that the timing of zygote division is an evolutionary strategy to ensure that the embryo receives adequate nutrition.

5. **Connecting Assertion and Reason**: The assertion and reason are closely related. The assertion highlights the timing of zygote division, while the reason explains that this timing is an adaptation to ensure the embryo's nutritional needs are met.

6. **Conclusion**: Both the assertion and the reason are true, and the reason provides a correct explanation for the assertion. Therefore, the correct answer is that both statements are true and the reason is the correct explanation for the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.