I've already answered this question. All I want to know is if my reasoning is correct.
Case 1:
$\ce{Rb+}$
$\ce{Na+} \leftarrow$ This ion is more strongly favored
Case 2:
$\ce{Mg^{2+}} \leftarrow$ This ion is more strongly favored
$\ce{Na+}$
Reasoning:
For the first case, my guess would have to be because the electrons are much closer to the center of the nucleus (the atomic radius of the atom is very small) and makes it much easier to interact the positive dipole end of the water molecule (the hydrogen molecules).
For the second case, the reason why the magnesium ion is more favored is because even though both ions have roughly the same molar mass, one is more positively charged than the other and thus is more likely to attract the negative dipole end of the water molecule (the oxygen molecule).
Is my reasoning justified or is there something in particular that I'm not paying attention to?