Here's why:

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

* Acids: Acids have a pH less than 7.

* Bases (alkalines): Bases have a pH greater than 7.

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

Since 6 is less than 7, a pH of 6 indicates an acidic solution.