If this propane tank is opened inside a house, the atoms in the tank immediately spread throughout the whole house. Propane is most likely a solid. liquid. gas. plasma.

The right option is; gas

Propane is most likely a gas.

Propane gas is a flammable hydrocarbon, and one of the liquefied petroleum gases. Propane is produced from petroleum refining and natural gas processing. Propane gas can be liquefied at very low pressures. Propane is commonly used as fuel in cooking, heating, and also for aerosol propellants, refrigerants, and in motor vehicles.