In which immunological technique does the random movement of antigen or antibody occur to form antigen-antibody complexes in semisolid medium?

The correct answer is immunodiffusion, which is a technique that relies on the random movement of antigens and antibodies as they diffuse through a semisolid medium, such as agar gel. In this process, when an antigen and a specific antibody come into contact within the gel, they can interact and form visible complexes. This can be observed as a precipitin line or zone where the two meet, indicating that the two components have reacted optimally.

Immunodiffusion is particularly useful for qualitative and quantitative analysis of different antigens and antibodies, enabling the assessment of their presence and concentrations in a sample. The movement through the semisolid medium allows for a clear visualization of this interaction, thus making it an important technique in immunology for diagnosing various diseases and conditions.

The other techniques listed serve different purposes in immunology. Western blotting is primarily used for the detection of proteins through gel electrophoresis followed by transfer to a membrane and probing with antibodies. Electrophoresis is a method for separating charged molecules based on their size and charge, not focusing on the random movement to form complexes as in immunodiffusion. Complement fixation is a classic serological test that measures the ability of antibodies to fix complement in the presence of specific