[A]: Lymphocytes develop in lymphoid tissue and involved in cell mediated and humoral immunity.
[R]: Lymphocytes are produced in primary lymphoid tissue (thymus, embryonic liver and adult bone marrow) and migrate to secondary lymphoid tissue (spleen and lymph nodes)

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the question regarding the assertion and reason about lymphocytes, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Lymphocytes develop in lymphoid tissue and are involved in cell-mediated and humoral immunity."
- **Analysis**: This is true because lymphocytes, which include B-cells and T-cells, play crucial roles in both types of immunity. B-cells are responsible for humoral immunity (producing antibodies), while T-cells are involved in cell-mediated immunity (attacking infected cells).

2. **Understanding the Reason**:
- The reason states that "Lymphocytes are produced in primary lymphoid tissue (thymus, embryonic liver, and adult bone marrow) and migrate to secondary lymphoid tissue (spleen and lymph nodes)."
- **Analysis**: This statement is also true. Lymphocytes are indeed produced in primary lymphoid organs (thymus for T-cells and bone marrow for B-cells) and migrate to secondary lymphoid organs (spleen and lymph nodes) where they can encounter antigens.

3. **Evaluating the Relationship**:
- Now we need to determine if the reason is the correct explanation of the assertion.
- The assertion describes the role of lymphocytes in immunity, while the reason describes where they are produced and how they migrate. The reason provides foundational knowledge about the origin and movement of lymphocytes, which supports the assertion regarding their function in immunity.

4. **Conclusion**:
- Both the assertion and reason are true, and the reason correctly explains the assertion.
- Therefore, the correct answer is: **Both assertion and reason are true, and reason is the correct explanation of assertion.**

### Final Answer:
The correct option is **1**: Both assertion and reason are true, and reason is the correct explanation of assertion.