What is the term for flammable gas that is liquefied under pressure?

The term for flammable gas that is liquefied under pressure is Liquefied Petroleum Gas (LPG). This gas is a mixture of propane and butane, both of which can be compressed into a liquid state under relatively low pressures. When stored in tanks, LPG remains in this liquefied form, making it easy to transport and store. Upon release from these tanks, it vaporizes into gas, which can then be used as fuel for heating, cooking, and other applications. This characteristic of being able to be liquefied under pressure is crucial for handling and usage, differentiating it from gases that remain in gaseous form at normal temperatures and pressures.

While natural gas is also a flammable gas, it primarily consists of methane and is not typically stored as a liquid. Acetylene, used mainly for welding and cutting, is a different type of gas with its own properties. Butane is a component of LPG but is not the specific term that describes a mixture of propane and butane when referring to flammable gas that is liquefied under pressure. Therefore, LPG is the correct answer as it encapsulates this combination of properties effectively.