Which functional group is characterized by a carbon double-bonded to an oxygen atom and single-bonded to a hydroxyl group?

The functional group described as having a carbon double-bonded to an oxygen atom and single-bonded to a hydroxyl group is characteristic of carboxylic acids. In this structure, the carbon atom is part of both a carbonyl group (C=O) and a hydroxyl group (–OH), which is the defining feature of carboxylic acids. The combination of these two elements results in the functional group denoted as –COOH. This structure not only imparts distinct chemical properties but also enhances acidity due to the ability of the hydroxyl group to donate a proton (H+).

In contrast, aldehydes contain a carbonyl group but lack the hydroxyl component, while ketones have a carbonyl group situated between two carbon atoms with no hydroxyl group present. Alcohols have hydroxyl groups attached to a carbon but do not possess the carbonyl component necessary for the classification as a carboxylic acid. Thus, the given description accurately matches the structure of a carboxylic acid, confirming its identification.