Final answer:
The pH of a substance is a measure of its hydronium ion concentration. Acidity is measured on a scale called the pH scale, which ranges from 0 to 14.
Step-by-step explanation:
The pH of a substance is a measure of its hydronium ion concentration. Acidity is measured on a scale called the pH scale, which ranges from 0 to 14. A pH value below 7 indicates an acidic solution, while a pH value above 7 indicates a basic (alkaline) solution, and a pH of 7 represents a neutral solution. The pH scale is logarithmic, meaning that each whole number decrease in pH represents a tenfold increase in acidity, and each whole number increase in pH represents a tenfold decrease in acidity.