The molecule H2 consists of two hydrogen atoms bonded together. It does not belong to any specific functional group in organic chemistry. Functional groups are specific groups of atoms that are responsible for the characteristic chemical reactions and properties of organic compounds.
In the case of H2, it is a diatomic molecule composed solely of hydrogen atoms. It is not considered an organic compound since it does not contain carbon. Organic compounds are compounds that contain carbon atoms covalently bonded to hydrogen and may also contain other elements such as oxygen, nitrogen, sulfur, and others. Functional groups in organic compounds typically consist of specific arrangements of atoms bonded to the carbon skeleton, such as hydroxyl (-OH), carbonyl (C=O), amino (-NH2), and many others.
However, in the context of organic chemistry, hydrogen atoms can be part of functional groups when bonded to carbon atoms within organic molecules. For example, hydrogen atoms are present in functional groups such as alkyl (-CH3), alkenyl (-CH=CH2), and alkynyl (-C≡CH) groups. These groups contain carbon-hydrogen bonds along with other atoms that contribute to the overall chemical properties of the organic molecule.