Why Does Ion Exchange Chromatography Depend on the PH of the Medium

Multiple Choice

Why does ion exchange chromatography depend on the pH of the medium?

A) The charge of each amino acid R group depends on the medium's pH.
B) The charge of each nucleic acid R group depends on the medium's pH.
C) The charge of each fatty acid R group depends on the medium's pH.
D) The charge of each terminal amino acid depends on the medium's pH.
E) The shape of each protein depends on the medium's pH.