Which functional group is present in alcohols?

The presence of the -OH group, also known as the hydroxyl group, is what characterizes alcohols. This functional group is responsible for the unique properties of alcohols, such as their ability to form hydrogen bonds, which contribute to their relatively high boiling points and solubility in water. When an organic compound has one or more -OH groups attached to a carbon atom, it is classified as an alcohol.

The other functional groups listed serve different roles in organic chemistry. The -NO2 group is a nitro group commonly found in nitro compounds, the -NH2 group represents an amine, and the -COOH group indicates a carboxylic acid. Each of these groups imparts distinct chemical behaviors and characteristics to their respective compounds, separating them from alcohols, which are specifically defined by the presence of the hydroxyl functional group.