This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Stain used in electron microscopy? 
Select and explain. 
A. 2.5% glutaldehyde, B. Phosphotungstic acid, C. Saffranin, D. Coomassie blue
B: Phosphotungstic acid
Answer: B: Phosphotungstic acid 
Explanation: Electron microscope: the technique of shadow casting with vapourised heavy metals has made pictures with good contrast and 3D effect possible. Another valuable technique in studying fine structure is negative staining with phosphotungstic acid REF:Ananthanarayan & Panicker's Textbook of Microbiology 8th Edition pg no: 13