Concept:EAN = (atomic number of metal) − (electrons lost to form the ion) + (electrons donated by ligands).Explanation:Atomic number of Co, Z=27Oxidation state of Co is +3, so electrons lost, X=3Six NH3 ligands donate 6×2=12 electrons, so Y=12Therefore,EAN=Z−X+Y=27−3+12=36Answer:36