$SnO_2$ forms a positively charged colloidal Sol in the basic medium why ?
$\begin{array}{1 1} \text{(a)$SnO_2$is amphoteric in nature. It reacts with acid eg HCl to form$SnCl_4$in the solution . The common$Sn^{4+}$ions are adsorbed on the surface of$SnO_2$particles giving the, a positive charge}\\ \text{(b)$SnO_2$reacts with a base eg.$NaOH$to form sodium stannate in the solution.The stannate ions are adsorbed on the surface of$SnO_2$particles giving them a Positive charge .} \\ \text{(c)$SnO_2$reacts with a base eg.$HCl$to form sodium stannate in the solution.The stannate ions are adsorbed on the surface of$SnO_4$particles giving them a positive charge .}\\\text{(d) None of the above} \end{array}$