What is a defining feature of hydroxoacids?

A defining feature of hydroxoacids is that the acidic proton is derived from a hydroxyl group. This characteristic is fundamental to the identity of hydroxoacids, as they consist of a central atom (often a non-metal) bonded to hydroxyl groups, where one of the hydrogen atoms from the hydroxyl group can dissociate as a proton, thereby exhibiting acidic behavior.

This feature clearly sets hydroxoacids apart from other types of acids that may not necessarily involve hydroxyl groups in their structure. In contrast, the presence of multiple oxo-groups is not a defining feature, as hydroxoacids may or may not contain these groups. Similarly, the notion that hydroxoacids are formed exclusively by non-metals is misleading, as some metal hydroxides can exhibit acidic properties when hydroxide ions are involved. Not all hydroxoacids are strong acids; many are weak acids, which means that associating them strictly with strong acidity does not accurately represent the diversity of their behavior.