The pH scale measures the concentration of hydrogen ions (H+) in a solution.

Here's why:

* pH stands for "power of hydrogen". It's a measure of the acidity or alkalinity of a solution.

* Acids release hydrogen ions (H+) when dissolved in water. The more H+ ions, the more acidic the solution.

* Bases (alkalines) accept hydrogen ions (H+) or release hydroxide ions (OH-). The more OH- ions, the more basic the solution.

So, while the pH scale is directly measuring H+ concentration, it indirectly reflects the balance between H+ and OH- ions in a solution.