A reddish brown sol is obtained by adding small quantity of FeCI3 solution to freshly prepared and well washed Fe(OH)3 ppt. Fixed layer and mobile layer can't be represented as

Fe(OH)3 sol adsorbs common ion of FeCl3 and Fe(OH)3 from  FeCl3, i.e. Fe3+ and positively charged sol is the fixed part of the electrical double layer. Thus, CI- (to balance charge of Fes3+) ions are on the mobile part of the electrical double layer.Fe(OH)3FixedFe3+:3Cl−Mobile