What is the term for an ion that carries a negative charge?

An ion that carries a negative charge is referred to as an anion. This terminology is derived from the fact that when atoms gain electrons, they acquire a negative charge due to the surplus of negatively charged electrons compared to positively charged protons in their nucleus. Since electrons are responsible for the negative charge, the overall charge of the ion becomes negative, hence the name "anion."

In contrast, a cation is an ion that has lost electrons and therefore carries a positive charge. The term "neutral ion" is not technically accurate, as ions are, by definition, charged species. Additionally, a radical ion typically refers to an ion that has unpaired electrons, which does not specifically address the charge of the ion. Thus, the most accurate term for a negatively charged ion is anion.