On which of the following properties does the coagulating power of an ion depend?

According to the Hardy-Schulze Rule:To coagulate a sol, the ion must have a charge opposite to that of the sol (sign matters).The coagulating power increases greatly with the magnitude of the charge on the ion.Example: For a negative sol, ${\text{Al}}^{3+}>{\text{Mg}}^{2+}>{\text{Na}}^{+}$.