Which of the following salt solutions would coagulate the colloid solution formed when \( \mathrm{FeCl_3} \) is added to \( \mathrm{NaOH} \) solution, at the fastest rate?
\( 10 \ \mathrm{mL} \) of \( 0.1 \ \mathrm{mol} \ \mathrm{dm}^{-3} \ \mathrm{Na_2SO_4} \)
\( 10 \ \mathrm{mL} \) of \( 0.15 \ \mathrm{dm}^{-3} \ \mathrm{CaCl_2} \)
\( 10 \ \mathrm{mL} \) of \( 0.2 \ \mathrm{mol} \ \mathrm{dm}^{-3} \ \mathrm{AlCl_3} \)
\( 10 \ \mathrm{mL} \) of \( 0.1 \ \mathrm{mol} \ \mathrm{dm}^{-3} \ \mathrm{Ca_3(PO_4)_2} \)