Recall the definitions of oxide character

• Basic oxides react with acids.
• Acidic oxides react with bases.
• Amphoteric oxides react with both acids and bases.

Check each option

A: $CaO$

• Calcium oxide is a metal oxide of an alkaline earth metal.
• Such oxides are generally basic.
• Example: $CaO + 2HCl \rightarrow CaCl_2 + H_2O$
• So, $CaO$ is not amphoteric.

B: $CO_2$

• Carbon dioxide is a non-metal oxide.
• Non-metal oxides are generally acidic.
• Example: $CO_2 + 2NaOH \rightarrow Na_2CO_3 + H_2O$
• So, $CO_2$ is not amphoteric.

C: $SiO_2$

• Silicon dioxide is also generally treated as an acidic oxide.
• It reacts with strong bases: $SiO_2 + 2NaOH \rightarrow Na_2SiO_3 + H_2O$
• So, $SiO_2$ is not amphoteric in this context.

D: $SnO_2$

• Tin(IV) oxide is a well-known amphoteric oxide.
• It reacts with acids as well as bases.
• With acid: $SnO_2 + 4HCl \rightarrow SnCl_4 + 2H_2O$
• With base: $SnO_2 + 2NaOH + 2H_2O \rightarrow Na_2[Sn(OH)_6]$
• Hence, $SnO_2$ is amphoteric.

Final conclusion

The amphoteric oxide among the given options is: $\boxed{SnO_2}$

Comparison with stored answer

• Derived answer: D
• Stored correct answer: D
• They match.