The mg2+ and na+ ions each have ten electrons. which ion would you expect to have the smaller radius? explain your choice

Mg2+ has the smaller radius because it has 12 protons where Na+ has 11. Because of Coulomb’s Law (F=kQ1Q2/r^2) the more protons there are, the more strongly the nucleus pulls on the electrons. This keeps the electrons closer to the nucleus and thus has a smaller radius than Na+ (which has fewer protons and thus a smaller attractive force between the protons and electrons).

Remember that rust prevented by placing a sacrificial electrode in electrical contact with the iron. the sacrificial electrode must be composed of a metal that  oxidizes  more easily than iron (that is, it must be below iron in table 18.1).

The answer is b. because when it leaves the bat, its bringing motion on where its going.