Seawater contains high concentrations of the ions Na+, Mg2+, and Cl−. Each of these ions, along with the noble-gas atom Ar, possesses a total of eighteen electrons.
a. Part 1: (a) Rank Na+, Mg2+, Ar, and Cl− from smallest to largest radius. Provide a complete justification that explicitly connects your ordering to relevant periodic properties.
b. Part 2: (b) Ion channels embedded in cellular membranes often discriminate between ions on the basis of size. Which of the four species listed would be expected to diffuse most rapidly through a narrow channel whose diameter is fixed? Explain your reasoning in terms of both particle size and electrostatic interactions with the channel walls.