Question

Oxide ions are also formed when aluminium oxide is dissolved. What is the formula of an oxide ion?

Answer 1

Oxygen, `Z=8`, commonly forms the oxide ion, `O^(2-)`.

Explanation:

We would have got the same formalism had we considered the formula of `Al_2O_3`, given that we know that aluminum commonly forms an `Al^(3+)` cation. Molten alumina is used in the preparation of aluminum metal; see this site for details.