Question

which is composed of alkenes?
welding torch fuel
polystyrene cups
propane gas
degreaser containing hexane

Explanation:

Alkenes are unsaturated hydrocarbons with carbon - carbon double bonds. Polystyrene is made from the polymerization of styrene (an alkene). Welding torch fuel often contains acetylene (an alkyne), propane is an alkane, and hexane is also an alkane.

Answer:

polystyrene cups