Atom is the
most basic unit of matter. They are the general term used to describe pieces of
matter. But a different kind of atom makes up an element. A combination of atom of different elements creates
a molecule. For example, you have water; it has a chemical formula of H2O. If you
separate H from O, you have two atoms. Two atoms for hydrogen and one atom for
oxygen. However, they are of different elements. And when you combine them to
form H2O, you create a molecule. The answer is A.
