Fire is a plasma, not a gas or a solid. It's a kind of transient state between being composed of the elements prior to ignition and the spent fumes (Smoke - solid particles and Gasses = Gas molecules.)
As did I. Turns out, fire is a catalyst in Sublimation, a term used in fire fighter hazardous materials training, where something goes from a solid to a gas without entering a liquid state.
Fire:; Objects can pass through it, so it is not solid; It consumes gas as energy, destroying the gas, so not a gas; Does not conform to the shape of a container, so it is not liquid; Is too cold to be plasma; What state of matter is it?