The following ions all have the same number of electrons: See attached file for full problem description.
Order them according to their expected size, and explain answer.
Here are some points regarding ion sizes:
* anions are larger than parent atoms
* cations are smaller than parent atoms
* atom size increases going down family (down a column in the periodic table). ion size also increases.
Thus the order is (from smaller to larger):
Ti < Sc < Ca < ...
The solution explains why anions and cations have such huge difference in their size.