* Water (H₂O) is a compound. It's made up of two hydrogen atoms and one oxygen atom.

* Sodium (Na) is an element. It exists as a single type of atom.

* Oxygen (O) is an element. It exists as a single type of atom.

* Iron (Fe) is an element. It exists as a single type of atom.

Therefore, the compound in the list is water (H₂O).