Here's why:

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

* Acidic: Substances with a pH below 7 are considered acidic.

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

* Alkaline (basic): Substances with a pH above 7 are considered alkaline (or basic).

Since 5.5 is less than 7, it falls within the acidic range.