UPSEE Solved Model Paper 5

In K4[Fe(CN)6] , K4 is a positive ion and Fe(CN)6 is a negative ion.
Charge of K4 is 4+, so charge of Fe(CN)6 is -4.
Let oxidation state of Fe be x.
[Fe(CN)6]4− ⇒ x + 6 x -1 = -4
x = -4 + 6 = +2
So, the oxidation number of Fe in K4Fe(CN)6] is +2.