If every oxygen ion (combined with an aluminum ion) has a charge of - 2, what must the charge of each aluminum ion be?

The charges should cancel out to 0. So if 1 oxygen ion combines with 1 aluminum ion and the oxygen ion starts with a - 2 charge, then the aluminum ion should have a + 2 charge. An uncharged aluminum ion would need to lose 2 electrons to get the + 2 charge