Answer
+2
+3
+6
+7
Work Step by Step
The oxidation number of the metal atom is simply the ionic charge present on the Calcium metal, 2+, because it is a free ion.
s has -2 charge so in order to balance the whole compound we should have the charge that is same as -6 but in positive, because charge of s is multiplied by coefficient 3.
Na = +1CrO = +6
MnO4- Oxidation number = +7
