How to find oxidation number of Fe in Na4[Fe(CN)6]?
Na4+ imparts a -4 charge outside the complex entity to allow neutrality of compound.
CN has an oxidation state of -1.So CN6 has oxidation state of -6. So for -4 to appear outside, the oxidation state of Fe must be +2.
-6+x=-4
x=-4+6=2