Determine the oxidation state of each transition metal in the following cmpds. (a) Na2MoO4 (b) KAuCl4 (c) MgWO4 and (d) Ni(CO)4

Answer 1

Na2MoO4. Here is how you do them.
Compounds must add to zero.
Na is +1, total Na is +2.
O is -4, total O is -8.
What does it take for Mo for the compound to be zero? Mo must be +6.
Here is a site that is a good one if you need some help on the rules.
http://www.chemteam.info/Redox/Redox-Rules.html

Answer 2

Na2MoO4 is +8