Which reaction is more common towards the end of a transfusion?

The correct answer is based on the fact that ABO incompatible transfusion reactions typically occur at the beginning or during the administration of the blood product due to the immediate immune response against incompatible blood types, leading to serious consequences if not recognized quickly.

In contrast, febrile, hemolytic, and allergic reactions can occur at various times during a transfusion, but research and clinical observations indicate that febrile reactions, while common, are more likely to manifest towards the end of a transfusion; they arise from the recipient's response to white blood cells or other components in the transfused blood. Allergic reactions are also often seen, but these tend to be less severe and can be more variable in timing. Hemolytic reactions, though serious, result specifically from immune responses to transfused red blood cells and can broadly occur if the blood was incompatible, but again, they often present immediately.

Thus, among the choices presented, ABO incompatible transfusion reaction is less likely to be observed toward the end of the process compared to reactions that are usually noted later on.