The active form of a hematoxylin that binds color to tissue is___________.

The active form of hematoxylin that binds color to tissue is hematein. Hematoxylin is a natural dye derived from the logwood tree, and when it undergoes oxidation, it is converted into hematein, which is the compound responsible for the staining of tissues in histological preparations. Hematein forms complexes with metal ions, particularly aluminum ions, which enhances the binding to nucleic acids in the tissue, resulting in a blue or purple coloration. This property makes hematein valuable in histology for visualizing cellular components, particularly nuclei, in tissue samples.

The other options do not relate to the active staining component of hematoxylin. Hematocrit refers to the ratio of the volume of red blood cells to the total volume of blood, hemoglobin is the oxygen-carrying protein in red blood cells, and hematogen is not a standard term used in the context of staining techniques.