Classify these oxides as acidic, basic, or amphoteric?

CO2, Cl207, K2O, Al2O3, BaO

Acidic oxides are the oxides of non-metals.
Basic oxides are the oxides of metals.
Amphoteric oxides are metallic oxides, which show both basic as well as acidic properties.

acidic oxides: CO2, Cl2O7
basic oxides : K2O, BaO
amphoteric oxide: Al2O3