What is an ion?

An ion is accurately defined as a charged particle that is formed when an atom or molecule gains or loses one or more electrons. This results in an imbalance between the number of protons, which are positively charged, and electrons, which are negatively charged. If an atom loses electrons, it becomes positively charged, known as a cation. Conversely, if it gains electrons, it becomes negatively charged, referred to as an anion. The formation of ions is crucial in various biological processes, including nerve impulse transmission and muscle contraction, as they facilitate the flow of electrical signals in cells.

In this context, a neutral particle would be an atom that has an equal number of protons and electrons, thus having no overall charge, which does not constitute an ion. Similarly, a particle found in the nucleus typically refers to protons and neutrons, which do not carry a charge in the same manner as ions. Lastly, a molecule that contains carbon, while chemically important, does not necessarily pertain to the definition of ions, as ions can form from any element based on the loss or gain of electrons, regardless of carbon's presence.