If Christopher is given with the same volume and thought that there's a difference in the concentration between the two solutions, he can device and experiment to calculate for Molarity. It has two components: the solvent (water) and the solute or concentration (the stuff dissolved in the water).
Doing this experiment let's him add add a substance to some specific volume of water to his solutions. As a result, the volume of the resulting solution will be different than the original volume. By this, he can detect which has more concentration. It is noteworthy that molarity is the moles of solute per liter of solution, not moles of solute per liter of solvent.
