Which of these acids is NOT used in decalcification/dehydration in tissue processing?

Hydrochloric acid is primarily known for its role in various chemical processes and reactions, but it is not typically utilized in the decalcification or dehydration phases of tissue processing. Instead, hydrochloric acid is more commonly used in analytical and laboratory techniques, such as pH adjustment or mineral analysis.

On the other hand, formic acid solution, aqueous nitric acid, and trichloroacetic acid are all known to effectively decalcify tissues by dissolving calcium salts. Formic acid is especially preferred in many histopathology laboratories because it allows for more gradual decalcification while preserving the tissue structure, making it ideal for histopathological evaluation. Aqueous nitric acid acts similarly, often being used in processes where rapid decalcification is desired. Trichloroacetic acid can also be employed for tissue fixation and is effective in decalcifying bone tissue or hard tissues.

Therefore, recognizing that hydrochloric acid does not serve the specific function of decalcification in histological processing helps to clarify why it is not part of the standard procedures employed in tissue preparation.