On the basis of the Hardy-Schulze rule,explain why the coagulating power of phosphate is higher than chloride.

(N/A) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency (charge).
$PO_{4}^{3-}$ has a valency of $3$,whereas $Cl^-$ has a valency of $1$.
Since the valency of the phosphate ion $(3)$ is greater than that of the chloride ion $(1)$,the coagulating power of phosphate is higher than that of chloride.