Consider a water sample containing Na+ ions. The sample is placed in contact with beads that have negative charges and the Na+ ions are attracted to the beads. How can Na+ ions be then removed?
a. Flow a polar liquid such as ethanol over the beads
b. Flow a weak acid solution such as CH3COOH over the beads
c. Flow a solution of MgCl2 over the beads
d. Heat the beads to evaporate Na+