Answer:
-2
Explanation:
Calcium is the element of second group and forth period. The electronic configuration of Calcium is - 2, 8, 8, 2 or [tex]1s^22s^22p^63s^23p^64s^2[/tex]
There are 2 valence electrons of Calcium.
Thus, calcium loses two electrons to sulfate ion and sulfate ion accepts these electrons to form ionic bond.
Calcium sulfate, [tex]CaSO_4[/tex] is formed when 2 valence electrons of calcium are loosed and they are gained by sulfate ion.
[tex]Ca^{2+}+SO_4^{2-}\rightarrow CaSO_4[/tex]
Thus, the charge on the sulfate ion is -2.