What is what state of matter is fire?

Fire isn't a state of matter in the same way solids, liquids, gases, and plasmas are. It's a chemical reaction, specifically a rapid oxidation process, usually involving a fuel source and an oxidant (typically oxygen). While it appears to have a form and occupy space, it doesn't have a fixed volume or shape like a solid, liquid, or gas.

The visible part of fire—the flames—is primarily composed of highly energized, incandescent gases. These gases are the products of combustion, such as carbon dioxide, water vapor, and various other molecules depending on the fuel source. These gases are indeed in the gas phase, but the fire itself is the process, not the gas. The hot gases are a consequence of the fire, not the fire itself.

Think of it like this: a boiling pot of water produces steam (a gas), but the boiling itself isn't a state of matter; it's a process that results in a change of state. Similarly, fire is a process that results in the production of hot gases. These gases, individually, are matter in a gaseous state, but the phenomenon of fire is not classifiable as a single state of matter.