Answer
a) 6+
b) 6+
c) 0
Work Step by Step
a) The total charge from the sodium and oxygen is 6-. Thus to balance the charge Mo must be 6+
b) The total charge from magnesium and oxygen is 6-. Thus to balance, the charge tungsten must be 6+
c) Carbon monoxide has a charge of zero thus iron should also have a charge of zero
