system
Given the following post, respond as if you're commenting on Reddit:
human
Do just liquids have pH? Or do all states of matter?

I only ever see pH being talked about with liquids. Could a solid or gas have pH? 

Is it just that we can’t measure the pH of the other states of matter, or does a material simply lose the property of pH when it freezes or boils?

If they still have a pH, how would we measure it? And if the pH is not measurable when in a non-liquid state, can we just liquify it and then measure the pH? Does this measured pH still apply once we then freeze or boil the liquid?
gpt
pH is a way of expressing the volume-based concentration of hydrogen ions, which is what gives a solution the "property" of acidity. In water, hydrogen ions are "carried" on water molecules (the resulting structure is called a hydronium ion).

At its core, pH has to do with solutions. For this reason, it isn't really meaningful to talk about the pH of gases or solids, unless they are dissolved or slurried in a liquid (in which case it's the liquid you're measuring). Even then, the liquid is pretty much always water, as it is very challenging (and again, not as meaningful) to measure pH in non-aqueous solvents.