Which of the following acids combines 10 mL of nitric acid and 5-10 mL of formalin in 100 mL of distilled water?

The combination of 10 mL of nitric acid and 5-10 mL of formalin in 100 mL of distilled water results in a solution that is essentially a nitric acid formaldehyde solution. This mixture often serves a specific purpose in histopathology, particularly in tissue fixation and preservation.

When nitric acid and formalin are combined, they engage in a chemical reaction that leads to the formation of a compound known as nitrosomethylurea, among other species, which is significant in the context of tissue fixation. The nitric acid acts as a strong acid, facilitating the fixation process by providing an acidic environment. Meanwhile, the formalin (which is a solution of formaldehyde in water) works as a fixative that preserves the morphological and structural integrity of the tissue samples.

Understanding this interaction is essential in histopathology, as the correct preparation of fixatives is crucial for obtaining high-quality tissue samples for microscopic examination. Therefore, identifying this specific combination as nitric acid formaldehyde is appropriate given its application in histological practices.