The gas most commonly used in balloons is helium. Helium is a colorless, odorless, and non-flammable gas that is lighter than air, allowing balloons filled with it to float. It is preferred over hydrogen because it is safe and poses no fire hazard. Helium is derived from natural gas sources and is considered a non-renewable resource; hence, its availability is subject to economic and environmental considerations. Due to its unique properties, helium is widely used not only for balloons but also in various scientific applications, such as cryogenics and gas chromatography.