The correct answer is: Carbon dioxide (CO2).
Carbon dioxide is a gas that is used in fire extinguishers to extinguish fires by displacing oxygen. It is also used in dry ice, which is used to keep food cold and to create special effects.
Carbon monoxide (CO) is a gas that is produced when carbon is burned in an incomplete combustion reaction. It is a colorless, odorless gas that is poisonous to humans.
Carbon suboxide (C3O2) is a gas that is produced when carbon monoxide is heated to high temperatures. It is a colorless, odorless gas that is also poisonous to humans.
Sulphur dioxide (SO2) is a gas that is produced when sulphur is burned. It is a colorless, odorless gas that is also poisonous to humans.
Carbon dioxide is the most common gas used in fire extinguishers because it is non-toxic and non-flammable. It is also effective at extinguishing fires because it displaces oxygen, which is necessary for combustion.