<prompt> The reaction between antibody and soluble antigen is demonstrated by -AgglutinationPrecipitationComplement fixation testHemagglutination test  <response>: When a soluble antigen companies with its antibody in the presence of electrolyte at a suitable temp pH the antigen-antibody complex forms an insoluble precipitate. Ref: Ananthanarayan Parkers textbook of microbiology 9th edition pg:105 