A certain road accident partient with unknown blood group needs immediate blood transfusion. His one doctor friend at once offers his blood. What was the blood group of the donor ?

Options

A. Blood group B
B. Blood group AB
C. Blood group O
D. Blood group A

Explanation

To determine the blood group of the doctor friend who donated blood to the accident patient with an unknown blood group, we need to understand the compatibility of blood groups based on the presence of antigens and antibodies.

### Step-by-Step Solution:

1. **Understanding Blood Groups**:
- There are four main blood groups: A, B, AB, and O.
- Each blood group has specific antigens on the surface of red blood cells (RBCs) and corresponding antibodies in the plasma.

2. **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.
- **Blood Group O**: Has no antigens and has both anti-A and anti-B antibodies.

3. **Compatibility for Blood Transfusion**:
- For a safe blood transfusion, the donor's blood must not have antigens that can react with the recipient's antibodies.
- Blood group O is unique because it has no antigens, meaning it can be donated to any blood group without causing an immune reaction.

4. **Conclusion**:
- Since the patient’s blood group is unknown and requires immediate transfusion, the safest option is to use blood group O.
- Therefore, the blood group of the doctor friend who donated blood must be **blood group O**.

### Final Answer:
The blood group of the donor (doctor friend) is **O**.

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