Which is not true regarding the pH scale?

The neutral pH at 25°C is 7.0.

Bases have a pH greater than 7.0.

The pH scale measures the hydronium ion concentration in solution.

When the concentration of hydroxide ions increases, the pH decreases.

The statement that is not true regarding the pH scale would be the final one. As the concentration of hydroxide ions in a corresponding solution increases, the pH would increase, as the solution becomes more basic and not as acidic. The pH values from 0-6 account or characterize a solution to be acidic, while from 8-14 would be basic. Increase in hydroxide will increase the pH from original value.