Option D shows correctly an ion pair and the correct formula for the ionic compound the two ions form.
Ion pairs of iron and oxygen react to form iron (III) oxide. The iron (III) oxide is one of the oxides of iron. The compound is usually attacked by acids and it is often called rust. It is used in the feedstock of the steel and iron industries. This means that the compound is used in the production of iron, steel, and many alloys.
