This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Prozone phenomenon is seen with - 
Select and explain. 
A. Same concentration of antibody and antigen, B. In antigen excess to antibody, C. Antibody excess to antigen, D. Hyperimmune reaction
C: Antibody excess to antigen
Answer: C: Antibody excess to antigen 
Explanation: Ans. is 'c' i.e., Antibody excess to antigen Zone phenomenono The amount of precipitate formed is greatly influenced by the relative proportions of antigens and antibodies.o Precipitation occurs most rapidly and abundantly in the zone of equivalence in which the antigen and antibody are present in optimal proportions.o If increasing quantities of antigens are added to the same amount of antiserum in different tubes and the amounts of precipitate in different tubes are plotted on a graph, the resulting curve will have three phases :