What is the purpose of using nitric acid in forensic investigations?

The use of nitric acid in forensic investigations is primarily associated with recovering serial numbers from firearms. Serial numbers are often intentionally defaced or removed to prevent the identification of a firearm's origin. When nitric acid is applied to the surface of the metal where the serial number has been altered or ground off, it can reveal the serial number by reacting with the metal. This reaction may differentially etch the areas where the serial number was originally stamped, leading to clearer visibility of the numbers, which can then be documented and used for identification purposes.

In the context of forensic science, being able to recover and read serial numbers is essential for police investigations, linking firearms to crimes, and establishing connections between suspects and their weapons. This technique is a crucial part of forensic procedures in maintaining the integrity of evidence and facilitating law enforcement efforts. Other options, while related to forensic science, do not align with the specific properties and applications of nitric acid as effectively as recovering serial numbers from firearms.