Here's why:

* R-COOH is the general formula for a carboxylic acid. The "R" represents a generic hydrocarbon chain (like a methyl group, CH3, or an ethyl group, CH2CH3).

* Carboxylic acids are characterized by the carboxyl group (-COOH). This group contains a carbonyl group (C=O) and a hydroxyl group (OH).

* The hydrogen atom attached to the oxygen in the carboxyl group is acidic. It can be readily donated as a proton (H+), making the compound an acid.

In summary: The presence of the carboxyl group (-COOH) makes R-COOH an acidic compound.