Hematein can be formed by the actions of air or light.

• A. True
• B. False
• C. Not applicable
• D. Both

Answer: (A)

Hematoxylin must be oxidized to its active form, hematein, to stain tissue effectively. This oxidation can occur through exposure to air or by light, which converts hematoxylin into hematein. Once formed, hematein pairs with a mordant (such as aluminum) to create a hematein–mordant complex that binds to nucleic acids in the nucleus, producing the characteristic blue‑purple stain. So the statement is true: both air and light can drive the formation of hematein, enabling the staining process.