Superoxides are a class of compounds that contain the superoxide ion (O2-). The superoxide ion is a diatomic oxygen molecule (O2) that has gained an extra electron, resulting in a negatively charged species. Superoxides are highly reactive and can participate in a variety of chemical reactions.

Among the options given, the compound KO2 (potassium superoxide) is the only one that is a superoxide. Let's examine each option in detail to understand why.

a) Na2O2 (sodium peroxide):
Sodium peroxide is an ionic compound that consists of sodium cations (Na+) and peroxide anions (O22-). The peroxide anion is not a superoxide because it contains two oxygen atoms in the -1 oxidation state, rather than one oxygen atom in the -1/2 oxidation state as found in superoxides.

b) K2O (potassium oxide):
Potassium oxide is an ionic compound composed of potassium cations (K+) and oxide anions (O2-). The oxide anion is not a superoxide because it contains two oxygen atoms in the -2 oxidation state.

c) KO2 (potassium superoxide):
Potassium superoxide is an ionic compound that consists of potassium cations (K+) and superoxide anions (O2-). The superoxide anion in KO2 contains one oxygen atom in the -1/2 oxidation state, making it a superoxide.

d) Fe3O4 (iron(II,III) oxide):
Iron(II,III) oxide, also known as magnetite, is a compound composed of iron cations in both the +2 and +3 oxidation states and oxide anions (O2-). The oxide anion in Fe3O4 is not a superoxide because it contains two oxygen atoms in the -2 oxidation state.

In summary, among the given options, only KO2 (potassium superoxide) is a superoxide because it contains the superoxide ion (O2-). The other compounds do not contain the superoxide ion and therefore are not superoxides.