Hardy-Schulze rule states that:
(a) non-electrolytes have better coagulating action on colloids than electrolytes
(b) sols are coagulated by effective ions whose charge is opposite to that of sol and the ions of higher charge are much more effective than the ions of lower charge
(c) charge of the ions has no effect on the coagulation of a sol
(d) sols are coagulated only by those ions whose charge is similar to that of the sol
(b) It is the definition of rule.