An electrical double layer is formed in the following in which mobile phase is positively charged

(1) AgI+AgNO3⟶[AgI]Ag+Fixed part⋮NO3−Mobile part(2) AgI+KI⟶[AgI]I−Fixed part ⋮ K+Mobile part(3) SnO2+2NaOH⟶Na2SnO3+H2OSnO2+Na2SnO3⟶SnO2SnO32−Fixed part ⋮ 2Na+Mobile part(4) SnO2+4HCl⟶SnCl4+2H2OSnO2+SnCl4⟶SnO2Sn4+Fixed part ⋮ 4Cl−Mobile part In NaOH1SnO2 is converted to SnO32− which is adsorbed on SnO2.  In HCl,SnO2 is converted to Sn4+ which is adsorbed on SnO2. Fixed part of the electrical double layer in sol while mobile part remains in medium.