Classify the oxygen species in each compound

Oxygen can exist in different anionic forms:

• Oxide: $O^{2-}$
• Peroxide: $O_2^{2-}$
• Superoxide: $O_2^{-}$

We identify each option using the known formulas.

Check each option

A: $KO_2$

• Potassium is $K^+$.
• So the oxygen part must be $O_2^-$.
• Hence, $KO_2$ is a superoxide.

B: $BaO_2$

• Barium is $Ba^{2+}$.
• So the oxygen part is $O_2^{2-}$.
• Hence, $BaO_2$ is a peroxide.

C: $SiO_2$

• This is silicon dioxide.
• Here oxygen is present as $O^{2-}$ bonded to silicon.
• Hence, $SiO_2$ is an oxide.

D: $CsO_2$

• Caesium is $Cs^+$.
• So the oxygen part must be $O_2^-$.
• Hence, $CsO_2$ is a superoxide.

Conclusion

The compound which is an oxide is: $\boxed{SiO_2}$ So the correct option is C.