c
With the exception of glycine all the \(19\) other common amino acids have a uniquely different functional group on the central tetrahedral alpha carbon

\(\mathop {\begin{array}{*{20}{c}}
{H\,\,\,\,\,\,\,\,\,\,\,\,}\\
{\,\,\,|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\
{H - C - COOH}\\
{\,\,|\,\,\,\,\,\,\,\,\,\,\,\,\,}\\
{\,N{H_2}\,\,\,\,\,\,\,\,}
\end{array}}\limits_{{\rm{Glycine}}} \)