This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Which of the following is a negative stain - 
Select and explain. 
A. Negrosin, B. Fontana, C. ZN stain, D. Albert stain
A: Negrosin
Answer: A: Negrosin 
Explanation: Negative staining is used in diagnostic microscopy, for contrasting a thin specimen with an optically opaque fluid. In this, the background is stained, leaving the actual specimen untouched, and thus visible. Whereas in 'positive staining', the actual specimen is stained.
Negative staining is typically performed using a black ink fluid such as nigrosin. The specimen, such as a wet bacterial culture spread on a glass slide, is mixed with the negative stain and allowed to dry. When viewed with the microscope the bacterial cells, and perhaps their spores, appear light against the dark surrounding background.