Which of the following reagents is used for blueing a hematoxylin-stained section?

The use of an alkaline solution for blueing a hematoxylin-stained section is based on the chemistry of staining protocols in histology. Hematoxylin, when bound to tissues, produces a purple coloration due to its interaction with nucleic acids. However, this color can often be enhanced or transformed into a more distinct blue shade, which is often more visually appealing and easier to interpret under the microscope.

An alkaline solution works effectively for this purpose because it raises the pH of the tissue section. This causes the hematoxylin to exhibit a change in its color properties, leading to the characteristic blue hue that is more distinguishable than the original purple stain. In practice, this is often achieved by using a dilute solution of sodium bicarbonate or ammonia, which effectively modifies the staining reaction by promoting the oxidation of hematoxylin and resulting in the desired blue coloration.

Overall, using an alkaline solution enhances the contrast and clarity of the staining, allowing for better visualization of the cellular structures within the prepared tissue section, which is a crucial factor in histological analysis and diagnosis.