Here's why:

* Carboxylic acids are organic compounds containing the carboxyl functional group (-COOH). This group has a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (-OH).

* Amino acids are organic molecules that contain both an amino group (-NH2) and a carboxyl group (-COOH).

* The carboxyl group is responsible for the acidic nature of amino acids. In aqueous solutions, the carboxyl group can donate a proton (H+), making the solution acidic.

Let me know if you have any other questions!