An anion is defined as what type of ion?

An anion is specifically defined as a negatively charged ion. This occurs when an atom or molecule gains one or more electrons, resulting in a surplus of negatively charged particles, which gives it a net negative charge.

In contrast, cations are positively charged ions formed when an atom or molecule loses electrons, leading to a higher number of positive charges compared to negative ones. Neutral ions do not exist since the very definition of an anion entails a net negative charge. Therefore, the only correct definition among the options is that an anion is a negatively charged ion.