Key Idea:- In peroxides, the oxidation state of O is - 1 and they give H2O2, with dilute acids, and have peroxide linkage. In KO2, +1+(x×2)=0 x=−21 (thus, it is a superoxide, not a peroxide.) In BaO2, +2+(x×2)=0x=−1 Thus, it is a peroxide. Only it gives H2O2 when reacts with dilute acids and has peroxide linkage as Ba2+[O−O]2− peroxide linkage In MnO2 and NO2,Mn and N exhibit variable oxidation states, thus, the oxidation state of O in these is -2 . Hence, these are not peroxides. Thus, it is clear, that among the given molecules only BaO2 is a peroxide.