This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cellular Pathology, Subject name: Pathology
Principle of Prussian blue stain: 
Select and explain. 
A. Ferrous to ferricyanide, B. Ferrocyanide to ferroferric cyanide, C. Ferroferriccyanide to ferrocyanide, D. Ferrocyanide to ferricferrocyanide
B: Ferrocyanide to ferroferric cyanide
Answer: B: Ferrocyanide to ferroferric cyanide 
Explanation: Ans. (b) Ferrocyanide to ferroferric cyanide(Ref: Dacie and Lewis Practical Haematology 11th ed, pg 338)Hemosiderin reacts with potassium ferrocyanide to form a blue compound, ferri ferrocyanide; this reaction is the basis of a positive Prussian-blue (Perls') reaction.