The universal blood donor group is:

Correct option is B

Blood transfusion compatibility is crucial in medicine.
· (a) AB+ – Incorrect, as it is the universal recipient, not donor.
· (b) O- – Correct, as it has no A/B antigens and no Rh factor, making it compatible for all blood types.
· (c) B+ – Incorrect, as it can only donate to B+ and AB+ groups.
· (d) A- – Incorrect, as it can donate only to A and AB groups.