Amine:
Amines are molecules that contain carbon-nitrogen bonds. The nitrogen atom in an amine has a lone pair of electrons and three bonds to other atoms, either carbon or hydrogen.
Functional group: NH2-R primary amine; NH-R secondary amine; N-R tertiary amine.
CH3CH2NH2 is the only one true. This is ethylamine
CH3CH2OH: OH- alcohol group
CH3CH2COOH: -COOH the functional group is a carboxyl group from a carboxylic acid.
CH3CH2SH: SH- this functional group is referred to as either a thiol group or a sulfhydryl group.
Answer: CH3CH2NH2 is an amine