In the Gram stain, iodine serves as the mordant.

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Multiple Choice

In the Gram stain, iodine serves as the mordant.

Explanation:
Iodine acts as the mordant in the Gram stain. It forms a crystal violet–iodine (CV–I) complex with the primary stain, increasing its size and binding strength so it is trapped in the cell wall of bacteria with thick peptidoglycan. This helps Gram-positive organisms retain the purple color during the decolorization step. In Gram-negative cells, the thinner peptidoglycan layer and outer membrane don’t retain the CV–I complex, so they are decolorized and then counterstained pink. So iodine’s role is to mordant, not to be the primary stain or the counterstain.

Iodine acts as the mordant in the Gram stain. It forms a crystal violet–iodine (CV–I) complex with the primary stain, increasing its size and binding strength so it is trapped in the cell wall of bacteria with thick peptidoglycan. This helps Gram-positive organisms retain the purple color during the decolorization step. In Gram-negative cells, the thinner peptidoglycan layer and outer membrane don’t retain the CV–I complex, so they are decolorized and then counterstained pink. So iodine’s role is to mordant, not to be the primary stain or the counterstain.

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