The answer is 4. Ion.
Dy definition, an ion is a charged atom or a non-zero charge. So if an atom is no longer neutral, it means that it is charged. We have two types of ions, a cation and an anion. A cation is positively-charged ion, this means that its protons outnumber the electrons. An anion is a negatively-charged ion, which means that the electron outnumber the protons.
