Final answer:
When oxygen reacts with metals, metal oxides containing the O²⁻ ion are usually formed.
Step-by-step explanation:
When oxygen reacts with metals, metal oxides are usually formed. Metal oxides contain the O2- ion.
For example, when magnesium reacts with oxygen, it forms magnesium oxide:
2Mg (s) + O2 (g) → 2MgO (s)
This reaction is a combination reaction where an element (magnesium) combines with oxygen to form an oxide (magnesium oxide).