Final answer:
The hydrocarbon not found in liquified propane gas is butane (C4H10). Propane gas is a light alkane consisting mostly of the propane molecule (C3H8) and smaller amounts of other hydrocarbons, with heavier alkanes like butane removed during refinement.
Step-by-step explanation:
The hydrocarbon that is not found in liquified propane gas is butane (C4H10). Propane, with the chemical formula C3H8, is a type of aliphatic hydrocarbon specifically called an alkane. Alkanes are saturated hydrocarbons with single bonds between carbon atoms. Propane is used in a variety of fuels and is one of the lighter alkanes. As propane gas is refined, it consists mostly of the propane molecule itself, although it may contain small amounts of other aliphatic hydrocarbons like ethane.
In liquified propane gas, the presence of heavier alkanes like butane is minimized because each hydrocarbon has its own range of boiling points, and during the refinement process, compounds with boiling points significantly different from propane are removed. This ensures that the liquified gas remains in a vaporized state over a range of temperatures suitable for the intended applications, like fuel for heating and engines.