The stain used to visualise mitochondria isA. Fast GreenB. SafraninC. AcetocarmineD. Janus Green

The correct answer is D. Janus Green.

Explanation:
Mitochondria are the powerhouse of the cell, and they play a critical role in energy production. To visualize mitochondria under a microscope, a specific stain is used to highlight their structure.

Janus Green is a dye that is specifically used to stain mitochondria. This dye works because it is selectively taken up by mitochondria due to their high oxidative activity. Janus Green changes color depending on the oxidative state within the mitochondria, making them visible under a light microscope.
Other options:

Fast Green: This is used to stain plant cell walls and proteins.
Safranin: This is a counterstain used in plant tissues to stain lignified tissues (like xylem) and is also part of the Gram staining technique for bacteria.
Acetocarmine: This stain is used to visualize chromosomes during cell division.
Thus, the stain specific for mitochondria is Janus Green.