What is an ion?

An ion is defined as a charged atom or molecule, which occurs when an atom gains or loses one or more electrons. When an atom loses electrons, it becomes positively charged and is referred to as a cation. Conversely, when an atom gains electrons, it becomes negatively charged and is known as an anion. This process results in an imbalance between the number of protons (positively charged) and electrons (negatively charged), thereby creating a charge.

Understanding this definition is crucial, as it distinguishes ions from neutral atoms, which have an equal number of protons and electrons, leading to no overall charge. Additionally, the other options mentioned do not accurately capture the essence of an ion, as they refer to different concepts that do not involve the charge state of the atom. An ion is fundamentally characterized by its charge, making the recognition of ions essential in various fields such as chemistry, physics, and biology, particularly in understanding electrolyte balance in biological systems.