Answer the following question given this paragraph: 

The strength of acids and bases is determined by the concentration of ions they produce when dissolved in water. The concentration of hydrogen ions in a solution is called acidity. It is measured by pH. A neutral substance has a pH of 7. An acid has a pH lower than 7, and a base has a pH greater than 7.


Q: The concentration of hydrogen ions in a solution is called?

 Choices:

- alkalinity

- alcohol

- moisture

- acidity

A:
acidity
