A colloidal solution is subjected to an electric field. The particles move towards anode. The coagulation of same sol is studied using $NaCl,BaC{l}_2\&AlC{l}_3$  solutions. The order of their coagulation power should be

As colloidal particles move towards anode so these particles are negatively charged and coagulated by cations of electrolyte.
According to Hardy Schulze rule,
Coagulation power  $\propto$ charge of ion
 Order of coagulation power is  $A{l}^{3+}>B{a}^{2+}>N{a}^{+}$