Answer:
D. An ion that is not directly involved in the reaction.
Explanation:
Spectator ions are ions that are not directly involved in a chemical reaction. They are commonly seen in complete ionic equations and are often taken out to make a net ionic equation because the ions aren't involved in forming the precipitate.
- Complete ionic equation: Gives all the ions participated in the chemical reaction, even spectator ions.
- Net ionic equation: Leaves out spectator ions so the equation only shows the ions that formed the precipitate.
For example, this is very useful when dealing with redox reactions because are complicated enough without spectator ions being in the way, so they help focus on those ions that actually form the precipitate.
