Answer:
An ion is an atom or group of atoms, that bears one or more positive/negative electrical charges. Ions are formed when a netrual atom loses or gains electrons. This loss/gain of electrons imparts a positive or negative charge to the neutral atom, making it an ion. The difference in the formation of a negative ion is that the atoms lose valence electrons to become positive ions (vice-versa with a positive ion, so the atom gains valence).
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