An enzyme that works best in an acidic environment would function optimally at a pH less than 7.

Here's why:

* pH scale: The pH scale measures the acidity or alkalinity of a solution.

* A pH of 7 is neutral (like pure water).

* A pH below 7 is acidic.

* A pH above 7 is alkaline (or basic).

* Enzyme activity: Enzymes are very sensitive to pH. Each enzyme has a specific pH range where it works most effectively. This is called the enzyme's optimum pH.

* Enzymes that work best in acidic environments have an optimum pH below 7.

* Enzymes that work best in alkaline environments have an optimum pH above 7.

Examples of acidic enzymes:

* Pepsin: An enzyme in the stomach that breaks down proteins, works best at a pH of around 2.

* Lysozyme: Found in tears and saliva, it breaks down bacterial cell walls, working best at a pH of around 5.