Is it appropriate to say "solid-in-gas solution" and "liquid-in-gas solution"?

Question

A number of books mention "solid-in-gas" and "liquid-in-gas" types of gaseous solutions.

However, for something to dissolve in a gas, it must be in its vapour phase. So, for instance, why wouldn't iodine vapours in air be a gas-in-gas solution?

Or, for that matter, since water vapour is gaseous water, why wouldn't water vapour in air be a gas-in-gas solution?

One reason I can think of is that we probably mention the main state these substances are in at room temperature. But then, water vapour also exists at room temperature (though water is obviously liquid).

How do I understand it?

Answer 1

Solid/liquid-in-gas solution is factical nonsense, being communication shortcut for a vapour of solid/liquid in a gas.

Solid sublimates/liquid evaporates into space not occupied by a condensed phase. Gas has nothing to do with that.

Mixture of gases is and is not solution, depending on the point of view.

It is a solution because it is a homogenous fluid mixture.

It is not a solution, because air/major gas does not participate in bringing the solid/liquid to gaseous phase at all. There is no action of dissolving, tearing a molecule from the condensed phase by molecules of gas. The vapour would be there even if there was no other gas at all. They just share common space, the gas being a bystander.

We do not say air is solution of oxygen and minor gases in nitrogen. There is no difference between "permanent gases" and vapours here.

Answer 2

You must look at the phases in your system. Whenever there is only one phase, but there are two or more chemical species, then you have a solution.

Beside this, all the rest is semantic. Some can be regulated by IUPAC, some not. Refer to air as a solution would sound unusual. A gas mixture - unless reacting to give a liquid or solid product - is always one phase, so the term gaseous solution isn't even considered by the IUPAC's definition of solution: https://goldbook.iupac.org/terms/view/S05746.

About "solid in gas" you are correct, once in the gas phases the iodine or naphthalene vapours aren't solid anymore. However, note that the same applies to sugar or salt in water. You can certainly speak of a solid (dissolved) in water although the actual solution obviously has no actual solid anymore, and even no salt but ions. In this case, the use is common because it is what operationally we do, we take a spoon of salt and dissolve it, even in the kitchen, and so we speak.

"Solid in gas (or liquid)" as it is and without context would mean smoke (or suspension), so we are not dealing with solutions.

I hope this is clear enough for you to understand that you were somehow over thinking the subject.