Metal compound solutions. The volumetric flasks contain solutions of an assortment of metals. The five at left are salts of transition metals, which tend to have coloured ions. From left, they are nickel, chromium, cobalt, vanadium and manganese. The three at right are the salts of non-transition metals, whose ions are generally colourless. From right they are calcium, sodium and magnesium. This difference is due to the arrangement of electrons in the ions.