Which reagent is used to convert hematoxylin to hematein?

• A. Sodium iodate
• B. Sodium nitrite
• C. Hydrogen peroxide
• D. Potassium permanganate

Answer: (A)

The main concept here is that hematoxylin must be oxidized to its active form, hematein, before it can form the dye complex that binds nuclei. Sodium iodate acts as a mild oxidizing agent to convert hematoxylin into hematein. Once hematoxylin is converted, it can form a stable complex with a mordant (usually aluminum) to produce the blue nuclear stain used in H&E.

Other reagents listed are not the standard activators for this conversion: for example, sodium nitrite is not used to oxidize hematoxylin, hydrogen peroxide is not the typical activator in this context, and potassium permanganate, while a powerful oxidizer, is not the routine reagent chosen for converting hematoxylin to hematein in standard practice.