Universal blood donor is:

Correct option is A

· Group O negative blood is considered the universal donor type because it has no A, B, or Rh antigens, minimizing the risk of adverse immune reactions.
· AB blood group is the universal recipient, not donor, as it has both A and B antigens but no antibodies against either.
· Option (c) and (d): Blood groups A and B can only donate to individuals with compatible antigens.
Additional Information:
· Rh factor is also considered during transfusion. O negative is the true universal donor as it does not have the Rh antigen.
· Emergency transfusions often use O negative when the recipient & blood type is unknown.