Which of the following is not a characteristic of an ion?

An ion is defined as an atom or a group of atoms that has an overall electric charge due to the loss or gain of one or more electrons. This charge can be either positive, resulting in a cation (when electrons are lost), or negative, resulting in an anion (when electrons are gained). This flexibility regarding the number of electrons leads to various ion types, making options a, c, and d accurately describe ions.

Option B, which states that an ion always consists of multiple atoms, is the correct answer to the question about which statement is not a characteristic of an ion. While there are indeed polyatomic ions (which consist of multiple atoms), many ions are monatomic, meaning they consist of a single atom. For instance, sodium (Na⁺) and chloride (Cl⁻) are examples of monatomic ions, clearly illustrating that ions do not always require multiple atoms to exist. Therefore, option B correctly highlights a non-characteristic trait of ions.