The staining of nuclei with hematoxylin is due to the presence of acidic groups in the DNA molecule. Hematoxylin, a basic dye, is attracted to these negatively charged groups and forms a complex with them. This complex is visible under a microscope as a blue-purple color.

The specific components of DNA that bind to hematoxylin are the phosphate groups on the deoxyribose backbone. These groups are arranged in a regular, repeating pattern that allows hematoxylin molecules to stack on top of each other and form a stable complex.

Other components of the nucleus, such as RNA and proteins, do not bind to hematoxylin as strongly as DNA does. This is because they do not have as many acidic groups as DNA does. As a result, they are not stained as intensely by hematoxylin and appear a lighter color under a microscope.

The ability of hematoxylin to stain nuclei selectively is an important tool in histology, the study of tissues. It allows scientists to visualize the nuclei of cells and to study their structure and function.