reactions are used to detect antibodies for relatively large pathogens

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Here is the complete question;

reactions are used to detect antibodies for relatively large pathogens, such as bacteria. For these tests, the antigen is mixed with the test sample at various dilutions. Reaction mixes are then monitored for the formation of visible aggregates.

Explanation:

AGGLUTINATION is the reaction used.

Agglutination is the reaction in which there is the clumping of particles. A agglutination reaction is the visible clumping of the bacterial cells as an antigen reacts with its corresponding antibody. This type is often used as an initial confirmation of specific pathogens. Agglutination tests is is used to detect antibody or antigen and it involves the  agglutination of bacteria, red cells, or antigen- or antibody-coated latex particles. It is therefor used for large pathogens like bacteria. In this reaction, antigens are introduced into various dilutions of antibodies in test tubes or surfaces of glass slides, visible clumping is observed which depends on the size of the antibodies, amount and acidity of the antibody molecule, time of incubation and as well as the environment of the reaction which includes optimum pH, protein concentration among others.  

pie chart because it is in percents ( % )

let that person have a turn to speak : )