Hydroxide (OH-) is not a liquid or gas. It is an ion, a charged atom or molecule.

Here's why:

* Hydroxide ions are formed when a water molecule (H2O) loses a proton (H+).

* Ions are always found dissolved in solutions or as part of ionic compounds.

* Solutions can be liquid, solid, or gas, but the hydroxide ion itself is not a separate phase of matter.

Examples:

* Sodium hydroxide (NaOH) is a solid ionic compound that dissolves in water to form hydroxide ions.

* Potassium hydroxide (KOH) is another example of a solid ionic compound containing hydroxide ions.

Let me know if you have any other questions!