Which statement about ferric chloride is accurate?

• A. It serves as both a mordant and an oxidizer.
• B. It is used mainly as a solvent for dyes.
• C. It is never used in staining protocols.
• D. It only mordants chromogens, not oxidizes.

Answer: (A)

Ferric chloride can both bind dyes to tissue (as a mordant) and participate in color development by oxidizing components in the staining process. As a mordant, iron(III) ions form dye–tissue complexes that help the dye adhere more firmly, intensifying the stain. As an oxidizer, it can oxidize substrates or reagents involved in color development, enabling a stable color to form. This dual functionality is why the statement stating it serves as both a mordant and an oxidizer is accurate.

It isn’t a solvent—it’s a salt that is dissolved in water to make staining solutions. It is indeed used in staining protocols, and it does more than just mordant; it can also act as an oxidizer, which is why the other options don’t fit.