Which of the following functional groups indicates the presence of a ketone?

The presence of a ketone is indicated by the functional group represented as -C=O. This functional group features a carbon atom double-bonded to an oxygen atom, which is characteristic of ketones. In ketones, the carbonyl group (C=O) is located between two carbon atoms, as opposed to aldehydes, where the carbonyl group is located at the end of a carbon chain (as seen with the -CHO group).

Understanding the nature of the carbonyl group is crucial in organic chemistry, as it plays a central role in the reactivity and properties of ketones. Ketones are important functional groups in various organic compounds and are often involved in reactions like nucleophilic addition due to the polarized nature of the carbonyl bond.

The other functional groups do not indicate the presence of a ketone. The -CHO group corresponds to aldehydes; the -COOH group indicates carboxylic acids; and the -OH group represents alcohols. Each of these functional groups has distinct properties and reactivity that differentiate them from ketones.