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The groups of atoms, which occur within the molecules and convene specific chemical characteristics to those molecules are known as functional groups. They are generally witnessed along the carbon backbone of macromolecules.

In a macromolecule, the functional groups are generally attached with the carbon backbone at one or distinct places along its ring or chain composition. Each of the four kinds of macromolecules possesses its own characteristic set of functional groups, which contributes towards its functionality.

Some of the essential functional groups found in the biological molecules are methyl, hydroxyl, amino, carbonyl, phosphate, carboxyl, and sulfhydryl. Thus, carbon can bond with hydroxyl, phosphate, and carbonyl as they are the functional groups.

The functional groups perform an essential activity in producing molecules like proteins, DNA, lipids, and carbohydrates. However, sodium is an element, a metal, it isnot a functional group.So, of the given options, sodium is an incorrect one.