Which of the following reagents acts as the mordant by reacting with crystal violet during the Gram staining procedure?

• A. Ethanol
• B. Safranin
• C. Carbol fuchsin
• D. Iodine

Answer: (D)

Verified step by step guidance

1. Understand the role of a mordant in the Gram staining procedure: a mordant is a substance that forms a complex with the primary stain, helping to fix it inside the bacterial cell wall.
2. Identify the primary stain used in Gram staining, which is crystal violet, and recognize that the mordant must interact with this dye to enhance its retention.
3. Review the list of reagents: Ethanol is a decolorizer, Safranin is a counterstain, and Carbol fuchsin is a stain used in acid-fast staining, so none of these act as mordants in Gram staining.
4. Recall that iodine is the mordant in Gram staining because it reacts with crystal violet to form a larger crystal violet-iodine complex that gets trapped in the thick peptidoglycan layer of Gram-positive bacteria.
5. Conclude that iodine is the reagent that acts as the mordant by reacting with crystal violet during the Gram staining procedure.