* Noun: This is the most common usage. It refers to a substance with a pH less than 7, typically having a sour taste and capable of reacting with bases.
* Example: "Lemon juice contains citric acid."
* Adjective: It can describe something as being sour or sharp.
* Example: "The food had an acid taste."
* Verb: Less common, but it can mean to treat with acid.
* Example: "The metal was acid-treated to prevent corrosion."
To determine the part of speech, you need to look at its function within the sentence.
