[tex]-NH_{2}[/tex] represents amine functional group and [tex]COOH[/tex] represents carboxylic acid functional group. When these both functional groups are substituted onto a single carbon atom, then amino acid is formed.
The organic compound consists of [tex]-NH_{2}[/tex] functional group and [tex]COOH[/tex] functional group with a side chain is said to be an amino acid.
A: amine group is [tex]-NH_{2}[/tex].
C: carboxylic acid group is [tex]COOH[/tex]
B: amino acid represents [tex]-NH_{2}[/tex] functional group and [tex]COOH[/tex] functional group which are substituted onto a single carbon atom.
D: carbohydrate: the general formula of carbohydrate is [tex](CH_{2} O)_{x}[/tex].
Hence, amino acid is the correct answer.
