Among the electrolytes $\mathrm{Na}_2 \mathrm{SO}_4, \mathrm{CaCl}_2 \quad…
Among the electrolytes $\mathrm{Na}_2 \mathrm{SO}_4, \mathrm{CaCl}_2 \quad \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3$ and $\mathrm{NH}_4 \mathrm{Cl}$, the most effective coagulating agent for $\mathrm{Sb}_2 \mathrm{~S}_3$ sol is
$\mathrm{Na}_2 \mathrm{SO}_4$
$\mathrm{CaCl}_2$
$\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3$
$\mathrm{NH}_4 \mathrm{Cl}$
Solution
$\mathrm{Sb}_2 \mathrm{~S}_3$ is an anionic $\mathrm{sol}_2$, therefore cation of highest valency ( $\mathrm{Al}^{3+}$ in the present case) would be most effective coagulating agent.