The coordination geometry of the central metal ion in the complex [Co NH3 6]Cl3 is octahedral. This is because there are six ammonia NH3 ligands surrounding the cobalt Co ion, forming six coordinate covalent bonds.The oxidation state of the central metal ion cobalt can be determined by considering the charges of the ligands and the overall charge of the complex. Ammonia NH3 is a neutral ligand, so it does not contribute to the charge of the complex. The complex has a charge of +3, which is balanced by the three chloride Cl- ions outside the coordination sphere. Therefore, the oxidation state of the cobalt ion is +3.