When you expose a wet iron nail (Fe) to the oxygen in air (O2), you will notice that rust, or iron oxide (Fe3O4), forms on its surface. Which of the following statements is true?

a. The elements iron in the nail and oxygen from the air combine to form the compound rust.

b. The compounds iron in the nail and oxygen from the air combine to form the element rust.

c. The elements rust in the nail and oxygen from the water combine to form the compound iron.

d. The elements iron in the nail and oxygen combine to form the mixture rust.