<prompt> Gram stain separates most bacteria into gram-positive bacteria and gram-negative bacteria. Which of the following stain is NOT used in gram staining?Methylene blueCrystal violetIodineSafranin  <response>: The Gram stain involves the following four-step procedure: The crystal violet dye stains all cells bluepurple. The iodine solution a mordant is added to form a crystal violet-iodine complex; all cells continue to appear blue. The organic solvent, such as acetone or ethanol, extracts the blue dye complex from the lipid-rich, thin-walled gram-negative bacteria to a greater degree than from the lipid-poor, thick-walled gram-positive bacteria. The gram-negative organisms appear colorless; the gram-positive bacteria remain blue. The red dye safranin stains the decolorized gram-negative cells redpink; the gram-positive bacteria remain blue. Ref: Levinson W. 2012. Chapter 2. Structure of Bacterial Cells. In W. Levinson Ed, Review of Medical Microbiology Immunology, 12e. 