The coordination number of the central metal ion in the complex [Fe CN 6]3- is 6. The coordination number refers to the number of ligands molecules or ions that are directly bonded to the central metal ion in a coordination complex. In the given complex, [Fe CN 6]3-, the central metal ion is Fe iron , and the ligand is CN- cyanide ion .The complex has a formula of [Fe CN 6]3-, which indicates that there are six cyanide ions CN- surrounding the central iron ion Fe . Each cyanide ion forms a coordinate covalent bond with the iron ion, resulting in a total of six bonds between the iron and the cyanide ions.Therefore, the coordination number of the central metal ion Fe in the complex [Fe CN 6]3- is 6. This means that the iron ion is surrounded by six cyanide ligands in its coordination sphere.