Functional group the atom or group of atoms, when attached with carbon chain and decide it’s chemical properties are called functionalgroups. Or a saturated hydrocarbon Is unreactive but if we introduced some other atom or group of atoms into it , the resulting compound becomes very reactive. This other atom or group of atoms present in the carbon compound is known as a functional group.
METHNOL ALCOHOL:- ETHANOL
ALDEHYDE:- METHANAL ETHANAL