Leg press, deadlifts, RDLs, lunges, leg extensions, leg curls, hack squats, split squats. All those will hit your legs, plus there variations. Do some sprints, run hills, stairs, those will hit your legs. Im sure there are more lifts I can't think of this second as well.
While natural gas occurs in nature as a mixture of methane and other gases, propane is actually a byproduct of both petroleum refining and natural gas processing.
Actually, that depends on what country you are in. In many countries, like the US and Australia, LPG is pure propane. However, New Zealand, Australia's close neighbour, has a mix. This article is a good read on the subject: Comparison between LPG & Natural Gas | Propane | Butane | Methane | LNG | CNG.