Mary could do two types of experiments
Type 1. She could hold the cation constant and vary the anion.
She could try solutions of NaCl, NaBr, NaI, Na₂SO₄, Na₃PO₄, etc.
These experiments would tell her which anions are the best conductors.
Type 2. She could hold the anion constant and vary the cation.
She could try solutions of NaNO₃, KNO₃, Mg(NO₃)₂, Ca(NO₃)₂, Al(NO₃)₃, etc.
These experiments would tell her which cations are the best conductors.
