The substance which can not be used for preparing H2O2 solution is

⇒ ⇒⇒⇒ compound which contain a peroxy bond will have the calculated oxidation number {assuming Ox.st of all "o" is (-2)]  of central atom will be grater than group no, which is impossible such compound will have peroxy bond.⇒ Calculated OX.no of Na in Na2O2 +2 group no . of Na →1So Na2O2 has a peroxy bond.Both the oxygen atom are peroxy oxygens with (-1) state.Thus actual Oxidation state of Na is (+1)⇒ In case of PBO2 the calculated oxidation state of "Pb" is "+4" it is equal to its group no. Therefore it can't contain peroxy linkage and hence on reaction with dilute acids it can't give Hydrogen peroxide.⇒ BaO2 also possess peroxy bond and hence it also give H2O2 on treatment with dilute acids.⇒ Where as PbO2 does not possess peroxy bond and hence it does not give H2O2 with dilute acids.