By the action of dilute sulphuric acid. Apaste of hydrated barium peroxide $(BaO_2.8H_2O)$ is prepared in ice – cold water and then added slowly to an ice-cold solution of $20\%\; H_2SO_4$
$BaO_2.8H_2O +H_2SO_4 \to BaSO_4+H_2O_2 +8H_2O$
The white precipitate of $BaSO_4$ is removed by filtration leaving behind a dilute solution $(5\%) \;of\; H_2O_2.$
In this method, anhydrous barium peroxide can not used since the precipitated $BaSO_4$ forms a protective layer around unreacted barium peroxide thereby preventing the further reaction
Hence (c) is the correct answer.