The correct option is Group O.
Explanation
The ABO blood grouping system is based on the presence or absence of two surface antigens, Antigen A and Antigen B, on the Red Blood Cells (RBCs). A transfusion is safe only if the donor's RBCs do not carry antigens that trigger an immune response from the recipient's antibodies.
- Group O (Universal Donor): Individuals with blood group O lack both Antigen A and Antigen B on the surface of their RBCs. Because there are no antigens for the recipient's immune system to attack, blood from a Group O donor can be transfused into individuals of any ABO group (A, B, AB, or O).
- Group A: Possesses Antigen A. It can only be donated to individuals with Group A or Group AB.
- Group B: Possesses Antigen B. It can only be donated to individuals with Group B or Group AB.
- Group AB (Universal Recipient): Possesses both Antigen A and Antigen B. While individuals with this blood type can receive blood from any group, they can only donate to other individuals with Group AB.
Key Takeaway: Blood Group O is known as the Universal Donor because its RBCs have no antigens. Blood Group AB is known as the Universal Recipient because its plasma has no antibodies against A or B antigens.