Weigert's Hematoxylin includes which mordant?

• A. Ferric Chloride
• B. Ammonium Aluminum Sulfate
• C. Mercuric Oxide
• D. Sodium iodate

Answer: (A)

The main idea here is that in Weigert's hematoxylin, the dye needs an iron mordant to form a stable complex that binds to nuclei and yields a deep blue-black stain. Ferric chloride provides that iron mordant, enabling hematoxylin to form the ferric-hematoxylin complex that strongly and durably stains chromatin. The other reagents are used in different stain formulations or roles: aluminum salts act as mordants in other hematoxylins, mercuric oxide is a mordant in some older stains but not this one, and sodium iodate is typically an oxidizing/differentiating agent rather than the mordant for Weigert's. Thus, ferric chloride is the correct mordant for Weigert's hematoxylin.