Here's why:

* pH Scale: The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 to 14.

* Acids: Acids have a higher concentration of hydrogen ions (H+) in solution. This makes the solution more acidic.

* Bases (alkalines): Bases have a lower concentration of hydrogen ions (H+) and a higher concentration of hydroxide ions (OH-). This makes the solution more alkaline (basic).

Therefore, a pH lower than 7 indicates a higher concentration of H+ ions, making the solution acidic.