Which of the following is a functional group present in carboxylic acids?

A functional group is a specific group of atoms or bonds within a molecule that determines the molecule's chemical properties and reactivity. Functional groups are usually classified based on the presence of a specific atom or group of atoms within the molecule. These are represented with the help of a suffix when attached to a carbon compound.

For example, for the alcohol group, we have -OH. Similarly for carboxylic acid, we have the suffix -COOH.