Which of the following techniques is classified as a negative staining method?

Explanation

Negative staining involves staining the background instead of the specimen itself. Among the listed options, the India ink smear is a classic example of negative staining, as it highlights capsules by leaving them unstained against a dark background. The other methods, such as Gram, Fontana, and Ziehl-Neelsen staining, are positive staining techniques where the cells or structures themselves are stained.