<prompt> An immunologist is conducting an experiment to understand precipitation reactions. He notes that on adding excessive amount of antibody to a serum sample containing small amount of antigen, the amount of precipitate formed is less, compared to adding smaller amount of antibody to the same sample. What is this phenomenon called?Pro-zone phenomenonZone of equivalencePost-zone phenomenonFlocculation phenomenon  <response>: Lattice hypothesis explains this: In precipitation reactions, the amount of precipitate formed is greatly influenced by the relative propoions of antigens and antibodies. Pro-zone phenomenon: It is caused by excessive antibody in the test system. Weak or even absent precipitation and a false negative test Zone of equivalence: Antigen and antibody are in optimum propoions and maximum precipitation occurs. Post-zone phenomenon: Presence of excessive antigen in the test system. Weaker or even absent precipitation Reference: Ananthanarayan and Paniker;s Textbook of Microbiology Tenth edition 