JEE Main · 2021 · 17 Mar 2021 · Shift 2 · Surface Chemistry

According to the Hardy-Schulze rule, the coagulating power of an ion is directly proportional to its charge. For coagulation of a negatively charged sol, cations are effective, and higher the charge on the cation, greater is its coagulating power. Among the given options, ${\mathrm{Ba}}^{2+}$ has the highest positive charge (+2), while ${\mathrm{Na}}^{+}$ has charge +1. The anions ${\mathrm{PO}}_4^{3-}$ and ${\mathrm{SO}}_4^{2-}$ would not be effective for coagulating a negative sol. Therefore, ${\mathrm{Ba}}^{2+}$ has the highest flocculating power.