The difference between magnesium and magnesium oxide:


Different composition elements: magnesium is composed of magnesium, while magnesium oxide is composed of magnesium and oxygen.
Magnesium is made up of atoms and magnesium oxide is made of ions.


Different colors: magnesium is silver white, magnesium oxide is white.
The chemical properties are different.
The reaction of magnesium with hydrochloric acid produces gas (hydrogen), while magnesium oxide reacts with hydrochloric acid without gas.