<prompt> Principle of Prussian blue stain:Ferrous to ferricyanideFerrocyanide to ferroferric cyanideFerroferriccyanide to ferrocyanideFerrocyanide to ferricferrocyanide  <response>: Ans. b Ferrocyanide to ferroferric cyanideRef: Dacie and Lewis Practical Haematology 11th ed, pg 338Hemosiderin reacts with potassium ferrocyanide to form a blue compound, ferri ferrocyanide; this reaction is the basis of a positive Prussian-blue Perls reaction. 