Here's why:

* The pH scale is logarithmic: This means that each whole number change in pH represents a tenfold change in acidity or alkalinity.

* Lower pH means higher acidity: A pH of 2 is four pH units lower than a pH of 6.

* Calculation: This translates to a difference of 10,000 times (10 x 10 x 10 x 10) in acidity!

Examples:

* pH 2: Strong acid like battery acid

* pH 6: Slightly acidic like rainwater or tea

In summary: A substance with a pH of 2 is 10,000 times more acidic than a substance with a pH of 6.