Which blood group in humans is the universal donor?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → O Group
A blood group is named after the antigens (A, B) on the red blood cells. The plasma carries antibodies against the antigen a person does not have, and these attack donated cells that carry it.
Red cells of group O have neither antigen A nor antigen B, so the antibodies of a receiver of any group find nothing to attack. Group O blood can therefore be given to people of every group: it is the universal donor (strictly, O negative, which also lacks the Rh antigen).
Why the other options are incorrect
Option (1) A Group — Incorrect. Its cells carry antigen A, which the anti-A antibodies of groups B and O attack.
Option (2) AB Group — Incorrect. Its cells carry both antigens, so it can be given only to group AB, which is the universal recipient.
Option (4) B Group — Incorrect. Its cells carry antigen B, which the anti-B antibodies of groups A and O attack.