Which of the following statements is incorrect?

Options

A. (a) A person of 'O' blood group has anti 'A' and anti 'B' antibodies in his blood plasma.
B. (b) A person of 'B' blood group can't donate blood to a person of 'A' blood group
C. (c) Blood group is designatrd on the basis of the presence of antibodies in the blood plasma
D. (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 based on our understanding of the ABO blood grouping system.

### Step-by-Step Solution:

1. **Understanding Blood Groups**:
- Blood groups in humans are classified mainly into four types: A, B, AB, and O.
- The classification is based on the presence or absence of specific antigens on the surface of red blood cells (RBCs).

2. **Identifying Antigens and Antibodies**:
- Blood group A has A antigens and anti-B antibodies.
- Blood group B has B antigens and anti-A antibodies.
- Blood group AB has both A and B antigens and no antibodies against A or B.
- Blood group O has no antigens and has both anti-A and anti-B antibodies.

3. **Evaluating Each Statement**:
- **Statement A**: "A person of O blood group has anti-A and anti-B antibodies in his blood plasma."
- This statement is **correct**. A person with blood group O does indeed have both anti-A and anti-B antibodies.

- **Statement B**: "A person of B blood group can't donate blood to a person of A blood group."
- This statement is **correct**. A person with blood group B has anti-A antibodies, which would react with A antigens in the recipient's blood.

- **Statement C**: "Blood group is designated on the basis of presence of antibodies."
- This statement is **incorrect**. Blood groups are designated based on the presence of antigens on the RBCs, not antibodies.

- **Statement D**: "A person of AB blood group is a universal recipient."
- This statement is **correct**. Individuals with AB blood can receive blood from any group without risk of agglutination because they have no antibodies against A or B antigens.

4. **Conclusion**:
- The incorrect statement among the options is **Statement C**. Therefore, the answer to the question is **C**.