${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$cannot be prepared by

Addition of ice cold ${\mathrm{H}}_{\mathrm{2}}{\mathrm{SO}}_{\mathrm{4}}\mathrm{to} {\mathrm{BaO}}_{\mathrm{2}}.8{\mathrm{H}}_{\mathrm{2}}\mathrm{O}$

Aerial oxidation of 2-ethyl anthraquinol

Addition of ice cold ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}{\text{to PbO}}_{\text{2}}$

Electrolysis of acidified  50% ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$at high current density followed by hydrolysis