Answer: Answer below
Explanation: pH is a measure of the acidity or alkalinity of a solution. What the pH scale measures is basically the concentration of hydrogen and hydroxyl atoms in a solution. So, the last option is the answer. Another thing to keep in mind is solutions with a pH under 7 are acidic, solutions with a pH of 7 are neutral, and solutions with a pH over 7 are alkaline or considered a base. I hope this helped! Good luck:)