What is an ion?

An ion is defined as an atom or molecule that has gained or lost one or more electrons, resulting in a net electric charge. When an atom loses electrons, it becomes positively charged and is termed a cation. Conversely, when an atom gains electrons, it becomes negatively charged and is referred to as an anion. This change in electron count disrupts the balance between protons (positively charged) and electrons (negatively charged) in the atom, leading to the development of an overall charge.

The other statements do not accurately describe an ion. For instance, a neutral atom, which has an equal number of protons and electrons, remains uncharged and is not considered an ion. A molecule consisting of two or more atoms refers to a distinct structural entity, typically covalently bonded, which is also not specific to ions. Lastly, an atom with an unstable nucleus relates to radioactive isotopes rather than the concept of ionic charge. Therefore, the key aspect of ions is their formation due to the gain or loss of electrons.