A bulb is wired in series with three separate charge-carrier cells, each tested one at a time: (I) a solid aluminum rod at 25 °C, (II) molten CaCl₂ at 900 °C, and (III) an aqueous solution of 1.0 M KCl at 25 °C. Rank the three cases from brightest to dimmest bulb illumination and provide one sentence explaining the trend in terms of mobile charge carriers.