Final answer:
In an antibody identification panel, 'ruling out' entails crossing out the antigens present on cells with a negative reaction, as this indicates the patient's serum does not contain antibodies against those antigens.
Step-by-step explanation:
"Ruling out" on an antibody identification panel involves crossing out the antigens present on cells that have a negative reaction. Therefore, the correct answer to the question is option 2) Crossing out the antigens present on cells that have a negative reaction. This process is part of the identification in which a patient's serum is tested against a panel of red blood cells with known antigenic profiles. If the patient's serum does not cause agglutination of red blood cells with particular antigens, it is concluded that the patient does not have antibodies against those antigens. These recognized patterns can then be used to identify possible antibodies in the patient's serum that could react during a blood transfusion or indicate an immune response to infection.