K4[Fe(CN)6]
Answer: potassium hexacyanoferrate(II)
Solution: potassium is the cation and the complex ion is the anion.
Since there are 4 K+ binding with a complex ion, the charge on the complex ion must be - 4.
Since each ligand carries –1 charge, the oxidation number of Fe must be +2.
The common name of this compound is potassium ferrocyanide.