Correct Answer - D
Peroxides are formed by group 2 elements wit increasing case and increasing stability as metal ions become larger because large cations stabilize lage anions by providing high lattice enthalpy. `BaO_(2)` is formed by passing air over `BaO` at `500^(@)C.SrO_(2)` is formed similarly but requires relatively higher temperature and pressure. `CaO_(2)` with `H_(2)O_(2)` and then dehydrating the product. Crude `MgO_(2)` is alos made using `H_(2)O_(2)` but no peroxide of Be is known,
