Potassium ferrocyanide, K4[Fe(CN)6], has a central iron ion that is coordinated with six cyanide ligands in an octahedral geometry. The oxidation state of the iron ion in potassium ferrocyanide is +2, hence has d2sp3 hybridised state. On applying C.F.T. it shows that all the 6 electrons of d subshell are present in the form of three pairs in t2g orbitals. Hence answer is 3.
