Which of the following statements is incorrect?

Options

A. A person of 'O' blood group has anti 'A' and anti 'B' antibodies in his blood plasma.
B. A person of 'B' blood group can't donate blood to a person of 'A' blood group.
C. Blood group is designated on the basis of the presence of antibodies in the blood plasma.
D. A person of AB blood group is universal recipient.

Answer

To determine which statement is incorrect, we will analyze each option provided in the question regarding blood groups and their characteristics.

### Step-by-Step Solution:

1. **Analyze Option A**:
- Statement: "A person of O blood group has anti-A and anti-B antibodies in his blood plasma."
- Explanation: This statement is correct. Individuals with O blood type do indeed have both anti-A and anti-B antibodies in their plasma, which is why they cannot receive blood from A or B blood types.

2. **Analyze Option B**:
- Statement: "A person of B blood group can't donate blood to a person of A blood group."
- Explanation: This statement is also correct. A person with B blood type has B antigens on their red blood cells and anti-A antibodies in their plasma. If they donate blood to a person with A blood type (who has anti-B antibodies), agglutination will occur due to the reaction between the anti-B antibodies and B antigens.

3. **Analyze Option C**:
- Statement: "Blood group is designated on the basis of the presence of antibodies in the blood plasma."
- Explanation: This statement is incorrect. Blood groups are designated based on the presence of antigens on the surface of red blood cells, not antibodies in the plasma. For example, blood group A has A antigens on RBCs, while blood group B has B antigens.

4. **Analyze Option D**:
- Statement: "A person of AB blood group is a universal recipient."
- Explanation: This statement is correct. Individuals with AB blood type have both A and B antigens on their red blood cells and do not have any anti-A or anti-B antibodies in their plasma, allowing them to receive blood from any blood type without risk of agglutination.

### Conclusion:
The incorrect statement is **Option C**, which claims that blood group designation is based on antibodies in the plasma.

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