anion
[C] Countable
pl: anions
This term describes a chemical species that has gained one or more electrons, resulting in a net negative charge. It is a technical term used almost exclusively in chemistry and physics to distinguish these particles from cations, which carry a positive charge. In a practical laboratory setting, anions are identified by their attraction to the anode during electrolysis. The word carries a neutral, scientific connotation and is used to describe the behavior of elements like chlorine or oxygen when they form salts.
Countable when referring to individual particles or specific types of chemical species in a solution.