What is an ion?

An ion is defined as an atom that has lost or gained one or more electrons, leading to a net electric charge. This charge imbalance occurs because electrons carry a negative charge; when an atom loses an electron, it becomes positively charged and is called a cation. Conversely, when an atom gains an electron, it acquires a negative charge and is referred to as an anion.

The other options do not accurately describe an ion. An atom with a neutral charge simply means it has an equal number of protons and electrons, thereby not being classified as an ion. An atom that consists only of neutrons would not be stable in most cases and does not fit the definition of an ion. Lastly, while stability is a property of some atoms, being completely stable does not equate to being an ion, since ions are characterized by their charge due to the loss or gain of electrons.