The particles of a particular colloidal solution of arsenic trisulphide `(As_(2)S_(3))` are negatively charged. Which 0.0005 M solution would be most effective in coagulating this colloidal solution. `KCl, MgCl_(2), AlCl_(3)` or `Na_(3)PO_(4)` ? Explain.

Explanation

Since `As_(2)S_(3)` is a negatively charged colloidal sol hence positively charged ion will cause its coagulation. By Hardy-Schulze rule "greater the charge on ion, greater the coagulating power to coagulate oppositely charged colloidal sol", hence out of `K^(+), Mg^(2+), Al^(3+)` and `Na^(+), Al^(3+)` would be most effective.