Why 'SnO2' forms a positively charged sol in solutions with 'pH<7' and negatively charged sol in solutions with pH>7'

Explanation

.A n s: operatornameSnO_2. is an amphoteric oxide
i) In .P^H<7. solutions.(acidic medium) .SnO_3. reacts with acid forming .SnCl_4 .. The .mathcalc o m^*. mon ion .S n^t+. is adsorbed on the surface of .SnO_2. particles, thus forming + ve charge.
ii) In basic medium ( .fP t^t>7. ) .operatornameSn O_2^n. form .Sn O_3^2-. which an adsorption on the
surface of .SnO_y. gives - ve charge
..
beginarrayl
SnO_2+2 NaOH rarrarrow 2 Na^++SnO_3+^--+H_2 O
SnO_2+SnO_3^2- rarrarrow SnO_2 * SnO_3^7-(- ve sol )
...