O2⁻²(aq) + 2H₂O(l)→ H₂O₂(aq) + 2OH⁻(aq)

This is a Bronsted-Lowry acid-base reaction where peroxide ion acts as a base, accepting two H⁺ from water molecules. Alkaline and alkaline earth peroxides contain this ion, so they react with water to produce hydrogen peroxide.

2O₂^- (aq) + 2H₂O(l) → H₂O₂(aq) + 2OH^-(aq)