What does the term "propane vapor" refer to?

The term "propane vapor" specifically refers to the gaseous form of propane when it is at atmospheric pressure. When propane is stored in tanks, it exists primarily as a liquid due to the pressure in the tank. However, when this liquid propane is released and the pressure decreases, it vaporizes into a gas. This gas is what we call propane vapor, which is essential in various applications such as heating, cooking, and fueling engines. Understanding this distinction is important for anyone working with propane, as it involves different handling and safety considerations compared to its liquid state.

The other choices do not accurately define what propane vapor is. The liquid state of propane at boiling point describes a different physical state. The compressed liquid state refers to propane under high pressure, while the solid state refers to propane at freezing temperatures, none of which describe the gas that results when propane is at atmospheric pressure.