AIPMT 2010 Physics and Chemistry Paper

In peroxides, the oxidation state of O is -1 and they give H2O2, with dilute acids, and have peroxide linkage. In KO31
+1+(X×2)=0
x=−‌

1

2

(thus, it is a superoxide, not a peroxide.)
In BaO2,‌‌+2+(x×2)=0
x=−1
Thus, it is a perioxide. 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.