chemistry?

The O-O bond in ⁻O-O⁻ is a covalent bond. (Don't make confusion that O²⁻ would make covalent bonds with other cation, i.e. Ca²⁺O²⁻)

Each O atom has 6 valence electrons (electrons in the outermost shell), and thus O⁻ has 7. Two O⁻ bonds together by sharing a pair of electrons to become a ⁻O-O⁻. It is a covalent bond because covalent bond is formed by sharing of electrons.

How could it possibly be ionic?