`SnO_2` forms a positively charged colloidal sol in the acidic medium and negatively charged sol in the basic medium. Explain.

Explanation

`SnO_(2)` is amphoteric with acid and base both. In acidic medium (say HCl) `Sn^(4+)` ion is formed which is preferentially adsorbed on `SnO_(2)` gicing positively charged colloidal sol:
`SnO_(2)+ 4HCl rarr SnCl_(4)+2H_(2)O`
`SnO_(2)+SnCl_(4) rarr [SnO_(2)]Sn^(4+)("positively charged")+4Cl^(-)`.