Which substances are added to a chromogen to enable it to retain its color in tissue?

The substance that is added to a chromogen to enable it to retain its color in tissue is indeed an auxochrome. An auxochrome is a functional group that does not have color on its own but enhances the color of a chromogen and helps in its binding to tissue components. This enhancement occurs because the auxochrome alters the electronic configuration of the chromophore, increasing the ability of the compound to absorb light and thereby reinforcing the chromogen's coloring properties.

In histopathology, the combination of a chromogen and an auxochrome is essential for creating stable, visible staining that remains in the tissue sections after preparation and examination. This is crucial in diagnosing various conditions through tissue analysis as it ensures that the stains will provide clear, reliable results when observed under a microscope.

Other options, while they might relate to the staining process in various ways, do not account for the role of auxochrome specifically in enhancing the color retention ability of a chromogen in tissues.