A substance that will make universal indicator turn orange is slightly acidic.

Here's why:

* Universal indicator is a mixture of different dyes that changes color depending on the pH of the solution.

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

* pH 0-6 is acidic

* pH 7 is neutral

* pH 8-14 is alkaline (basic)

* Orange on the universal indicator scale corresponds to a pH of around 4-5, which indicates a slightly acidic solution.

Examples of substances that would turn universal indicator orange:

* Vinegar (acetic acid)

* Lemon juice (citric acid)

* Tomato juice

* Weak solutions of hydrochloric acid (HCl)

Let me know if you'd like more details about the pH scale or universal indicator!