# How do the elements iron and oxygen combine?

Well clearly you need the metal, $\text{iron}$, and the oxidant, $\text{oxygen}$..........and these are the 2 elements.
Of course iron oxide is a very broad church; there are simple oxides of iron, $F e O$, and $F {e}_{2} {O}_{3}$, and higher order iron oxides, i.e. $F {e}_{3} {O}_{4}$, which is a mixed oxide of $F {e}^{I I}$ and $F {e}^{I I I}$. See here for more details.