Here's why:

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

* Acids: Acids are substances that release hydrogen ions (H+) when dissolved in water.

* pH and H+ concentration: The more hydrogen ions present in a solution, the lower the pH.

* Neutral: A pH of 7 is considered neutral (like pure water).

* Bases: Bases (also called alkalis) have a pH greater than 7 and contain more hydroxide ions (OH-) than hydrogen ions.

So, acids have a high concentration of H+ ions, resulting in a lower pH value.