William finds : piece of pure iron in his garden. After a few days, the iron begins to rust. What are the two types of substances involved in the rusting process of iron? Iron is
with one kind of atom that combines with oxygen from the air to form rust (iron oxide). Rust contains two types of atoms, which means it is

1) Element, compound

2) Iron is an element as it contains only one kind of atom, which combines with the oxygen from the air to produce rust, that is, iron oxide. The rust comprises two kinds of atoms, which signifies that it is a compound. A compound refers to a molecule that comprises at least two types of atoms. In the case, iron oxide is a compound as it comprises Fe and O atom.

real, smaller and upside-down.   so the answer should be b.