Here's why:
* Calcium (Ca) is an alkaline earth metal in group 2 of the periodic table. It has a +2 charge when it forms ionic compounds.
* Polonium (Po) is a metalloid in group 16 of the periodic table. It has a -2 charge when it forms ionic compounds.
Since they have equal and opposite charges, they combine in a 1:1 ratio to form a neutral compound.
