Which property of a liquid is measured by its volatility?

Volatility is a property of a liquid that describes its tendency to vaporize. Specifically, it refers to the liquid's vaporization rate, which is how readily a liquid turns into vapor at a given temperature and pressure. A liquid with high volatility will evaporate quickly, producing a significant amount of vapor at lower temperatures, while a liquid with low volatility will evaporate slowly.

This concept is crucial in understanding fire behavior because volatile substances can lead to quick ignition and rapid fire spread due to their ability to generate flammable vapors. Other properties such as density, temperature, and pressure are important in their own contexts but do not directly pertain to the measure of how quickly a liquid turns into vapor. Therefore, the vaporization rate is the correct answer as it directly encompasses the aspect of volatility in liquids.