PH stands for potential hydrogen.
pH can be accurately tested using acid-based indicators since it is a part of the pH of something itself. (acid and bases) The indicators themselves work when the acidic properties of the indicator begins to dissolve and form ions which gives the color indicating the pH.
Well, TECHNICALLY, the periodic table is "based" upon a whole myriad of characteristics. But if you're talking about the consecutive arrangement of elements...it would be B, the atomic number.