The scale that describes the acidity of a solution as a number is the pH scale.

Here's a breakdown:

* pH stands for "power of hydrogen".

* It measures the concentration of hydrogen ions (H+) in a solution.

* The scale ranges from 0 to 14.

* Lower pH values (0-6) indicate a more acidic solution.

* Higher pH values (8-14) indicate a more basic (alkaline) solution.

* A pH of 7 is considered neutral.

For example:

* Lemon juice has a pH of around 2, making it acidic.

* Pure water has a pH of 7, making it neutral.

* Bleach has a pH of around 12, making it basic (alkaline).