Question

what is funtional group

Answer 1

Functional group is a atom or group of atom in its molecules largely determine it chemical properties

Answer 2

Functional groups are a set of atoms/molecules which when attached to a hydrocarbon chain, results in a specific set of characteristic chemical properties for that compound.
Example, carboxylic group, which imparts acidity. Alcoholic group (OH), Amino group (NH2), etc.