A. The unicellular zygote developes into a multicellular embryo during embryogenesis.
R. Organogenesis forms an important part of the process of embryogenesis.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion
B. It both Assertion & Reason are true but the reason is not the correct explanation of the assertion
C. If Assertion is true statement but Reason is false
D. If both Assertion and Reason are false statements

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "the unicellular zygote develops into a multicellular embryo during embryogenesis." This means that the zygote, which is a single cell formed by the fusion of sperm and ovum, undergoes a series of divisions and differentiations to become a multicellular structure known as an embryo.

2. **Understanding the Reason**: The reason states that "organogenesis forms an important part of the process of embryogenesis." Organogenesis is the process where the three germ layers (ectoderm, mesoderm, and endoderm) formed during gastrulation develop into various organs and tissues.

3. **Analyzing the Process of Embryogenesis**:
- The zygote undergoes cleavage, resulting in multiple cell divisions that lead to the formation of a morula (a solid ball of cells).
- The morula develops into a blastocyst (a hollow ball of cells).
- The blastocyst then transforms into a gastrula, where the three germ layers are formed.
- Organogenesis occurs after the gastrula stage, where these germ layers differentiate into specific organs.

4. **Evaluating the Truth of Each Statement**:
- The assertion is true because it accurately describes the transformation of the zygote into a multicellular embryo.
- The reason is also true as organogenesis is indeed a crucial part of embryogenesis.

5. **Determining the Relationship Between Assertion and Reason**:
- While both statements are true, the reason does not serve as a direct explanation for the assertion. The assertion describes the overall process of developing from a zygote to an embryo, while the reason focuses specifically on organ formation, which is a later stage in the embryogenesis process.

6. **Conclusion**: Since both the assertion and reason are true but the reason does not explain the assertion, the correct answer is that both statements are true, but the reason is not the correct explanation of the assertion.

### Final Answer:
Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.