What is the term used for a positively charged ion?

A positively charged ion is called a cation. This term is derived from the Greek word "kation," which means "going down." In the context of chemistry, cations are formed when an atom loses one or more electrons, resulting in a net positive charge. The loss of negatively charged electrons outweighs the positive charges from protons in the nucleus, leading to this overall positive charge.

The other terms mentioned in the prompt refer to different concepts. An anion, for example, is a negatively charged ion, formed when an atom gains electrons. A neutral atom is one that has an equal number of protons and electrons, resulting in no overall charge. A metal ion generally refers to a ion derived from a metal which can be either a cation or an anion, but in this case, without specifying the charge, it does not specifically denote a positively charged ion. Therefore, cation is the precise term to describe a positively charged ion.