Agglutination occurs in blood present in a test tube. This indicate

Options

A. Antibodies are present in plasma
B. Antigens are present on R.B.C.
C. Antigens are present in plasma
D. Antibodies are present on R.B.C.

Answer

To solve the question regarding agglutination in blood present in a test tube, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Agglutination**:
- Agglutination is the clumping of cells, such as red blood cells (RBCs), due to the interaction between antigens and antibodies.

2. **Identifying Components**:
- In blood, antigens are present on the surface of RBCs, while antibodies are found in the plasma.

3. **Mechanism of Agglutination**:
- When an antibody encounters its specific antigen, it binds to it, leading to the clumping of cells. This is known as isoagglutination when it occurs with blood cells.

4. **Analyzing the Options**:
- **Option A**: Antibodies are present in plasma - This is true, but it does not explain the agglutination directly.
- **Option B**: Antigens are present on RBCs - This is true and is the reason for agglutination.
- **Option C**: Antigens are present in plasma - This is incorrect in the context of blood agglutination.
- **Option D**: Antibodies are present on RBCs - This is incorrect; antibodies are not found on RBCs.

5. **Conclusion**:
- Since agglutination occurs due to the interaction of antibodies with antigens on the RBCs, the correct answer is **Option B: antigens are present on RBCs**.

### Final Answer:
**B. Antigens are present on RBCs.**

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