Among the following oxides of p-block elements, the number of oxides having amphoteric nature is: \[\text{Cl}_2\text{O}_7, \, \text{CO}, \, \text{PbO}_2, \, \text{N}_2\text{O}, \, \text{NO}, \, \text{Al}_2\text{O}_3, \, \text{SiO}_2, \, \text{N}_2\text{O}_5, \, \text{SnO}_2\]