Final answer:
An acid is likely used for etching metals for printing purposes.
Step-by-step explanation:
The likely use of an acid is etching metals for printing. Acids are corrosive substances that can etch metal surfaces, creating grooves for printing processes. One example of an acid used for this purpose is nitric acid, which is commonly used in the printing industry. Acid etching allows for precise and detailed prints to be made on metal surfaces.