The reaction between antibody and soluble antigen is demonstrated by -: (A) Agglutination, (B) Precipitation, (C) Complement fixation test, (D) Hemagglutination test
Answer is B. 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 & Parker's textbook of microbiology 9th edition pg:105