Here's why:

* The pH scale measures acidity and alkalinity: It ranges from 0 to 14.

* Lower numbers indicate higher acidity: A pH of 0 is the most acidic, while a pH of 14 is the most alkaline (basic).

* Neutral pH is 7: This is the pH of pure water.

So, acids like lemon juice or vinegar will have a pH lower than 7.