Kaplan Nursing Entrance Exam Practice 2025 – Comprehensive Prep

An ion is best defined as an atom that has a net electrical charge, which occurs when the number of protons (positively charged) and electrons (negatively charged) are not equal. When an atom gains or loses one or more electrons, it does not change the number of protons in its nucleus but results in a charge: if electrons are lost, it becomes positively charged (a cation), and if electrons are gained, it becomes negatively charged (an anion). This definition highlights the fundamental characteristic of ions—their charge—distinguishing them from neutral atoms, which have equal numbers of protons and electrons.

In contrast, a neutral atom does not have any overall charge due to having the same number of protons and electrons. An atom with a different number of neutrons refers to isotopes, which do not involve changes in electrical charge and pertain to variations in atomic mass. Lastly, a combination of two or more atoms describes a molecule, which again deviates from the definition of an individual ion. Therefore, the defining feature of an ion is its net electrical charge.