A solution containing equal numbers of hydrogen ions (H+) and hydroxide ions (OH-) is called a neutral solution.

Here's why:

* pH scale: The pH scale measures the acidity or alkalinity of a solution.

* Neutral pH: A neutral solution has a pH of 7.

* Equal concentrations: In a neutral solution, the concentration of H+ ions and OH- ions is equal.

Let me know if you'd like to know more about pH or acidity and alkalinity!