Final answer:
The oxide ion is larger in size compared to the oxygen atom because ions become larger when electrons are added.
Step-by-step explanation:
When an atom loses one or more electrons, the resulting ion becomes smaller. If electrons are added to the atom, the ion becomes larger. Cations, which are positively charged ions, are always smaller than the neutral atom. Anions, which are negatively charged ions, are always larger than the neutral atom. Therefore, the size of the oxide ion is larger than that of the oxygen atom.