This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2019, Subject name: Microbiology
Elek's gel precipitation test used for diagnosing: 
Select and explain. 
A. Corynebacterium Jakeium, B. Corynebacterium diphtheriae, C. Clostridium tetani, D. Clostridium perfringens
B: Corynebacterium diphtheriae
Answer: B: Corynebacterium diphtheriae 
Explanation: Elek's gel precipitation test is an example of double diffusion in two dimensions. It is used to demonstrate C. dipthariae. Precipitation band: If the strain is toxigenic, the toxin diffuses in the agar, meets with the antitoxin and produces arrow-shaped precipitation band. Nontoxigenic stain will not produce any precipitation line. The precipitate lines would fuse with each other if the toxins produced by die strains are identical.