What is an ion?

An ion is defined as an atom that has gained or lost one or more electrons, resulting in a net charge. This process of gaining electrons creates a negatively charged ion, known as an anion, while losing electrons leads to a positively charged ion, referred to as a cation. The fundamental characteristic of ions is that they are no longer electrically neutral due to the imbalance between the number of protons and electrons.

The other options do not accurately describe an ion. For instance, a molecule made from multiple elements refers to a compound rather than a single atom with a charge. An uncharged atom indicates a neutral state where the number of protons equals the number of electrons, which is not the case for ions. Lastly, a type of isotope involves variations of an atom based on the number of neutrons, independent of the electron configuration that defines ionization. Understanding these distinctions is crucial in disciplines such as chemistry and physics, where the behavior of ions plays a significant role in chemical reactions and electrical conductivity.