A water molecule that loses a hydrogen ion (H+) is called a hydroxide ion, which is represented as OH-.

Here's why:

* Water molecule: H₂O

* Hydrogen ion: H+

* Hydroxide ion: OH-

When a water molecule loses a hydrogen ion, it becomes negatively charged because it now has one more electron than proton. This negatively charged species is the hydroxide ion.

This process is often referred to as dissociation of water. It's a reversible reaction, meaning the hydroxide ion can also gain a hydrogen ion to form water again.