Step-by-step explanation:
A functional group is a collection of atoms within molecules that bind together to react in predictable ways.
The functional group tell us how a compound react and, also, the chemical properties of such compound
Below are the functional group of some compound
Alcohol
The functional group of alcohol is ---- OH
Example: Ethanol
Ester
The functional group of Ester is --O--
Example: Ethyl ethanoate
Aldehyde
The functional group of aldehyde is
Example: Vanillin