${\mathrm{BaO}}_2+{\mathrm{H}}_2{\mathrm{SO}}_4⟶{\mathrm{BaSO}}_4+{\mathrm{H}}_2{\mathrm{O}}_2$

In the above method of preparation of ${\mathrm{H}}_2{\mathrm{O}}_2$, now-a-days ${\mathrm{H}}_3{\mathrm{PO}}_4$ (conc.) is used instead of conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$, because :

For given reaction,

${\mathrm{BaO}}_2+{\mathrm{H}}_2{\mathrm{SO}}_4⟶{\mathrm{BaSO}}_4+{\mathrm{H}}_2{\mathrm{O}}_2$

${\mathrm{H}}_3{\mathrm{PO}}_4$(conc.) is used instead of concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ Because ${\mathrm{H}}_2{\mathrm{SO}}_4$   catalyzes the decomposition of ${\mathrm{H}}_2{\mathrm{O}}_2$. Hence option B is Correct.