$ The reproductive cells in the testes are called spermatocytes.
! Labia majora is a part of the external genitalia of human females.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the assertion and reason question regarding the reproductive cells in the testes and the labia majora, we will follow these steps:

### Step 1: Analyze the Assertion
The assertion states that "the reproductive cells in the testes are called spermatocytes."
- **Evaluation**: This statement is correct. In the male reproductive system, spermatocytes are indeed the cells that undergo meiosis to form sperm.

### Step 2: Analyze the Reason
The reason states that "labia majora is a part of the external genitalia of human females."
- **Evaluation**: This statement is also correct. The labia majora are indeed part of the external genitalia in females.

### Step 3: Determine the Relationship
Now we need to determine if the reason is a correct explanation of the assertion.
- **Evaluation**: While both statements are correct, the reason does not explain the assertion. The assertion is about spermatocytes in the male reproductive system, while the reason discusses a part of the female reproductive system. Therefore, they are unrelated.

### Step 4: Choose the Correct Option
Based on the evaluations:
- Option A states both are correct and the reason explains the assertion. This is incorrect.
- Option B states both are correct but the reason does not explain the assertion. This is correct.
- Option C states the assertion is correct and the reason is wrong. This is incorrect.
- Option D states both are wrong. This is incorrect.

Thus, the correct answer is **Option B**: Both the assertion and reason are correct, but the reason is not the correct explanation of the assertion.

### Summary of the Solution
1. The assertion is correct: spermatocytes are the reproductive cells in the testes.
2. The reason is correct: labia majora is part of the external genitalia in females.
3. The reason does not explain the assertion.
4. The correct answer is Option B.