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 plama
D. A person of AB blood group is universal recipient

Answer

To determine which statement is incorrect regarding blood groups, we will analyze each option provided.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- **Statement:** A person of O blood group has anti-A and anti-B antibodies in his blood plasma.
- **Analysis:** 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 can only receive blood from other O type donors.

2. **Analyze the Second Statement:**
- **Statement:** A person of B blood group can't donate blood to a person of A blood group.
- **Analysis:** This statement is also correct. A person with B blood type has anti-A antibodies, which would react against A antigens present in the blood of an A blood group recipient.

3. **Analyze the Third Statement:**
- **Statement:** Blood group is designated on the basis of the presence of antibodies in the blood plasma.
- **Analysis:** This statement is incorrect. Blood groups are determined by the presence of antigens (A and B) on the surface of red blood cells, not by the antibodies in the plasma. The presence of antibodies is a result of the blood group type but does not define it.

4. **Analyze the Fourth Statement:**
- **Statement:** A person of AB blood group is a universal recipient.
- **Analysis:** This statement is correct. Individuals with AB blood type have both A and B antigens and do not have anti-A or anti-B antibodies, allowing them to receive blood from any ABO type.

### Conclusion:
The incorrect statement is the third one: "Blood group is designated on the basis of the presence of antibodies in the blood plasma."

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