Which of the following functional group of carbon does NOT contain oxygen?

Halogen

The correct answer is option 2. Halogen.

The functional group of carbon that does NOT contain oxygen is Halogen.

Halogen functional groups involve the attachment of a halogen atom (such as fluorine, chlorine, bromine, or iodine) to a carbon atom. Unlike the other options listed (alcohol, aldehyde, and ketone), halogen functional groups do not contain oxygen atoms. They are characterized by the presence of a carbon-halogen bond.