Final answer:
The oxide ion has a charge of -2, balancing out the positive charges of metal ions in compounds to maintain electrical neutrality.
Step-by-step explanation:
The charge of an oxide ion is -2. This is because the oxide ion has two more electrons than protons, resulting in a negative charge. In compounds like titanium dioxide (TiO2), the titanium (Ti4+) must balance the charge of the oxide ions to make the compound electrically neutral. The formula TiO2 indicates that there are two oxide ions for every titanium ion, so with each oxide ion having a charge of 2-, the total negative charge is -4, which is balanced by the 4+ charge of the titanium ion. Therefore, TiO2 is an electrically neutral compound.