The concentration of hydrogen ions in a solution is measured by pH.

Here's a breakdown:

* pH stands for "power of hydrogen."

* It's a logarithmic scale that indicates the acidity or alkalinity of a solution.

* Lower pH values indicate a higher concentration of hydrogen ions (H+), meaning the solution is more acidic.

* Higher pH values indicate a lower concentration of hydrogen ions, meaning the solution is more alkaline (or basic).

For example:

* A pH of 1 is very acidic (strong acid)

* A pH of 7 is neutral (like pure water)

* A pH of 14 is very alkaline (strong base)