The correct option is D K4[Fe(CN)6]<K3[Fe(CN)6]<K2C2O4<KBr
Fe(OH)3 sol is positively charged sol. So, coagulation (flocculation) is due to anions.
Flocculation value is defined as the minimum concentration of an electrolyte required to cause the coagulation of the sol.
Coagulating power α 1Flocculation value
With respect to anions Br−,C2O−24,[Fe(CN)6]3−,[Fe(CN)6]4−,
the increasing order of coagulation value is
K4[Fe(CN)6]<K3[Fe(CN)6]<K2C2O4<KBr