Which state of matter is fire?

Most ordinary flames are a complex mixture of chemical species undergoing combustion to form new compounds, macroscopic soot molecules that ride convection currents and undergo visible blackbody radiation, and atoms that are thrust into their excited states by heat and collisions and release visible light upon relaxation. Therefore, most flames will contain the gas and solid states of matter.

It is possible for regions of ordinary flame to qualify as plasma. It should be noted that this is a hotly debated question and a satisfactory answer will depend on the details of whatever flame is under consideration.

A necessary condition for a plasma state is a collection of free positive and negatively charged particles that can rearrange to oppose external applied fields. More specifically, for something to be considered a plasma, several conditions must be satisfied, one of which is a very small Debye length, which is taken as, roughly, the depth to which an external electric field can penetrate the substance.

If we take this as a standard for a plasma, ordinary flame will contain extremely low density plasma with the exact level dependent on the flame temperature. Even flames of 1500 deg C will not be hot enough to generate significant regions of high density ionization, and therefore, very little plasma.

There are beautiful videos of flames conducting electricity and being bent by external applied fields. These are often accompanied by claims for the plasma nature of flame. However, it is likely that the charged particles in the flames are a result of the applied field ionizing the gas molecules on its own.

The comprehensive answer is close to what some have said, fire is a process that includes several states of matter and many interesting phenomena, including the relaxation of excited gas atoms and incandescent soot. Ordinary flame contains very low density thermal plasma at the hottest regions of flame. In very hot flames, the density of ionization may become high enough to form higher density plasmas, but as we've seen, the devil is in the details.

Therefore, most flames contain the gas, solid, and to some extent, plasma states.

Plasma is the wrong answer, fire is not a state of matter, it is a state in reaction, plasma state is a state of matter where the electrons are free from the nucleus, present in the stars and in experimental stations with temperatures over 100,000 Kelvin, where in the stars the enormous temperatures and pressures, the core fusses the lighter elements such as hydrogen into heavier elements such as helium, realising energy, creating a energy vs gravity battle. In high mass stars this process fuses helium into even higher elements such as carbon, oxygen, nitrogen, all the way until iron, where the star can no longer fuse, and it dies in a explosion called as supernova spilling all the heavier elements into space, while the star core becomes a neutron star, pulsar or black hole. The heavy elements mix with gass clouds called nebulas creating new stars with orbiting planets and new life evolving in those planets, where the cycle repeats again.

Fire is a state of chemical reaction, where energy is released by the oxidation process or reaction of the fuel with atmospheric oxygen. In this process heat is released, the heat has temperature. All bodies have temperature, and by Planck's law radiate electromagnetic waves. The human body radiates infra red waves which can be detected by IR cameras. Lava or melted Iron in a furnace looks red due to the temperatures around 1000 Celsius which give out visible red light. A incandescent lamp gives out visible light duet to 3400C on the tungsten filament without UV radiation, the sun gives out visible light along with UV rays due to 5000C surface temperature. The fire from a burning wood looks red due to the heat being released by the reaction in visible light by the surrounding atmosphere where the reaction takes place.

For me, the answer is actually none of the above. Fire is not a state of matter but a reaction. Like acid melting something or the neutralization of a base and acid forming a salt.

For the most part, fire is a mixture of hot gases. Flames are the result of a chemical reaction, primarily between oxygen in air and a fuel, such as wood or propane. In addition to other products, the reaction produces carbon dioxide, steam, light, and heat. If the flame is hot enough, the gases are ionized and become yet another state of matter: plasma.

plasma is the 4th state of matter . and the other 3 are solid,liquid and gas.

so the answer is all of the rest