Can someone explain why B is the answer? The mark scheme says because Ca has the most postive charge but I thought Cl- will be the smallest as it has less shielding and has the greatest nuclear charge..
Ca2+ has the electron configuration of Argon, but with 2 more protons.
K+ and S2- have the same number of electrons as argon. In fact all of choices have the same number of electrons, but calcium has the most protons, therefore highest nuclear charge and therefore smallest ionic radius.
The overall charge on an ion has NOTHING to do with its ionic radius. Ionic radius depends only on the distance between the nucleus and the valence electrons (ie how many shells it has) and the nuclear charge (how many protons it has). This is a very common misconception!