What does the term "natural gas" refer to?

The term "natural gas" specifically refers to a gaseous fossil fuel that is primarily composed of methane (CH4). This distinction is crucial because it highlights the fundamental difference between natural gas and liquefied petroleum gas (LP gas), which consists mainly of propane and butane. Natural gas is formed from the remains of ancient marine organisms and is primarily found in underground reservoirs. It is used for a variety of applications, including heating, electricity generation, and as a raw material in the production of chemicals.

The other options represent concepts that do not accurately define natural gas. For example, liquid propane is an aspect of LP gas, while synthetic gas is typically produced from coal or biomass rather than being a natural resource. Additionally, describing natural gas as a renewable energy source would be misleading, as it is a fossil fuel formed over millions of years and is not renewable in the way that solar or wind energy is. Thus, the accurate characterization of natural gas as primarily methane differentiates it clearly from other gases and fuels.