Which of the following stains is used for determination of cytochrome oxidase activity in the cell?

The correct option is A Janus green B
The enzyme cytochrome oxidase is a large transmembrane protein complex found in bacteria and the mitochondrion of eukaryotes. It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane. Janus green B selectively stains mitochondria.

Golgi apparatus, nuclear chromatin in a dividing cell can be stained by methylene blue. Neutral Red dye or Congo Red dye can be used to stain yeast cells.

So, the answer is C.