Which of the following is not attached to the central carbon atom in an amino acid?
an oxygen
an amino functional group
a carboxyl functional group
a side chain ("r group")

An oxygen is not attached to the central carbon atom in an amino acid.

Explanation:

To understand this, we need to look at the simple molecular structure of amino acids. The basic structure of amino acid consists of an amine , a carboxyl functional groups.

There is also a R-Group for a particular amino acid on the side chain of it. Although oxygen is one of the key constituents of amino acid it is not directly attached with the central carbon atom in an amino acid.

the answer is :