Which blood group is determined by the ability to produce anti-H antibodies?

The Bombay phenotype is unique in that individuals with this blood group lack the H antigen, which is the precursor to the A and B antigens found on red blood cells. Because of this absence, individuals with the Bombay phenotype produce anti-H antibodies, which react against the H antigen. This phenomenon is particularly interesting because individuals with the Bombay phenotype can only receive blood from other Bombay phenotype donors, as their anti-H antibodies would cause a severe transfusion reaction if they received standard blood products (from groups A, B, AB, or O) that contain the H antigen.

In contrast, blood group O individuals have the H antigen present but do not express A or B antigens; they produce antibodies against A and B but not against H. Those with group AB express A and B antigens on their red cells and do not produce any anti-A or anti-B antibodies, nor do they produce anti-H antibodies since they have the H antigen present. Group A individuals have A antigens and also do not produce anti-H antibodies, as they have the H antigen as well. Thus, the production of anti-H antibodies is a distinctive characteristic of the Bombay phenotype, making it the correct answer.