What defines an ion?

An ion is specifically defined as an atom that has either lost or gained one or more electrons, resulting in a net electrical charge. This means that if an atom loses electrons, it becomes positively charged, and if it gains electrons, it becomes negatively charged. Therefore, the correct definition of an ion directly aligns with the concept of a charged atom due to the imbalance between the number of protons (which are positively charged) and electrons (which are negatively charged).

The other options do not accurately capture the essence of what an ion is. A molecule with no charge refers to neutral compounds that have an equal number of protons and electrons. A compound made of two different elements describes the composition of a molecule rather than the electrical properties of an atom. An uncharged atom pertains to any atom that does not have a net charge, which is not in line with the definition of an ion. Thus, the emphasis on the electrical charge aspect is what makes the definition of an ion precise and accurate.