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

(1) $\mathrm{AgI}+{\mathrm{AgNO}}_3⟶\underset{\mathrm{Fixed} \mathrm{part}}{\left[\mathrm{AgI}\right]{\mathrm{Ag}}^{+}}⋮\underset{\mathrm{Mobile} \mathrm{part}}{{\mathrm{NO}}_3^{-}}$

(2) $\mathrm{AgI}+\mathrm{KI}⟶\underset{\mathrm{Fixed} \mathrm{part}}{\left[\mathrm{AgI}\right]{\mathrm{I}}^{-}}⋮\underset{\mathrm{Mobile} \mathrm{part}}{{\mathrm{K}}^{+}}$

(3) ${\mathrm{SnO}}_2+2\mathrm{NaOH}⟶{\mathrm{Na}}_2{\mathrm{SnO}}_3+{\mathrm{H}}_2\mathrm{O}$

${\mathrm{SnO}}_2+{\mathrm{Na}}_2{\mathrm{SnO}}_3⟶\underset{\mathrm{Fixed} \mathrm{part}}{\left[{\mathrm{SnO}}_2\right]{\mathrm{SnO}}_3^{2-}}⋮\underset{\mathrm{Mobile} \mathrm{part}}{2{\mathrm{Na}}^{+}}$

(4) ${\mathrm{SnO}}_2+4\mathrm{HCl}⟶{\mathrm{SnCl}}_4+2{\mathrm{H}}_2\mathrm{O}$

${\mathrm{SnO}}_2+{\mathrm{SnCl}}_4⟶\underset{\mathrm{Fixed} \mathrm{part}}{\left[{\mathrm{SnO}}_2\right]{\mathrm{Sn}}^{4+}}⋮\underset{\mathrm{Mobile} \mathrm{part}}{4{\mathrm{Cl}}^{-}}$

$\text{ In }{\mathrm{NaOH}}_1{\mathrm{SnO}}_2\text{ is converted to }{\mathrm{SnO}}_3^{2-}\text{ which is adsorbed on }{\mathrm{SnO}}_2\text{. }$

$\text{ In }\mathrm{HCl},{\mathrm{SnO}}_2\text{ is converted to }{\mathrm{Sn}}^{4+}\text{ which is adsorbed on }{\mathrm{SnO}}_2\text{. }$

Fixed part of the electrical double layer in sol while mobile part remains in medium.