Answer:
The answer is a pH scale.
Step-by-step explanation:
The pH of a solution is a measure of its acidity or alkalinity (base) and the pH scale ranges from 0 to 14. Also, a pH indicator is called litmus paper ( a paper treated with natural water-soluble dye, to test how much acid or base (alkalinity) is in a solution! (hope this helps and I found this by searching it up but I tried to reword it to avoid plagarism)