Understand that a functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule.
Recall that alcohols are organic compounds characterized by the presence of a hydroxyl group, which consists of an oxygen atom bonded to a hydrogen atom.
Identify the hydroxyl group as \(-\mathrm{OH}\), where the oxygen is single-bonded to a carbon atom in the molecule and also bonded to a hydrogen atom.
Compare this to other functional groups: the amino group is \(-\mathrm{NH}_2\), the carbonyl group is \(\mathrm{C}=\mathrm{O}\), and the carboxyl group is \(-\mathrm{C}=\mathrm{O}\mathrm{OH}\).
Conclude that the defining functional group of alcohols is the hydroxyl group \(-\mathrm{OH}\).