Final answer:
The ABO blood group A1 will have the weakest reaction to anti-H lectin because it has a high amount of A antigens, meaning less unmodified H antigen is available for anti-H lectin to react with.
Step-by-step explanation:
The question regards the ABO blood group systems and their reactions to anti-H lectin. Anti-H lectin is known to interact with the H antigen, which is a precursor to the A and B antigens on red blood cells. In the context of the ABO blood groups, individuals with group O (which lack both A and B antigens) would have the most H antigen present, therefore having a stronger reaction to anti-H lectin. Conversely, individuals with A1 blood type have a high amount of A antigens, which means less H antigen because it is converted into A antigen. Hence, blood group A1's reaction will be the weakest with anti-H lectin, because most of the H antigen has been modified to an antigen leaving less H antigen available to react with the anti-H lectin.