Question

In the coordination compound K4[Fe(CN)6] What is the oxidation number of Fe?

Answer 1

The K stands for potassium, which usually has a +1 charge. There are 4 of them, totaling +4 charge. Therefore the coordination complex must have a -4 charge for the total compound to have a zero charge. Since each cyanide ligand has a -1 charge, the central metal iron must have a +2 charge. So the signifigance goes beyond just the potassium, because the total formula then tells you what the valence of the Fe is in this compound, potassium ferrocyanide.