Which of the following oxides is amphoteric in character?

CaO is basic as it form strong base Ca ${\left(OH\right)}_2$ on reaction with water.

$CaO+H_{2}O\to Ca{\left(OH\right)}_2$                                               

 $C{O}_2$     is acidic as it dissolves in water forming unstable carbonic acid. $H_{2}O+C{O}_2\to H_{2}C{O}_3$

 Silica  $\left(Si{O}_2\right)$is insoluble in water and acts as a very weak acid,

$Sn{O}_2$ is amphoteric as it reacts with both acid and base.

$\begin{array}{l}Sn{O}_2+2H_{2}S{O}_4\to Sn\left(S{O}_4\right)+2H_{2}O\\ Sn{O}_2+2KOH\to K_{2}Sn{O}_3+H_{2}O\end{array}$