Explanation:
Atomic number of calcium is 20 and its electronic configuration is 2, 8, 8, 2.
Since it has two extra electrons, therefore, it donate these electrons to an electron deficient atom that needs only two electrons to complete its octet.
Oxygen atom has electronic configuration 2, 6. Hence, it is the atom that needs two electrons to complete its octet. So, it forms a compound of calcium oxide (CaO).
Thus, oxygen will most likely ionically bond with in a 1:1 ratio with [tex]Ca^{2+}[/tex].