What does vapor pressure indicate?

Vapor pressure is a measure of the pressure exerted by a vapor in equilibrium with its liquid or solid phase in a closed system. This indicates how easily a substance can evaporate at a given temperature. The correct interpretation of vapor pressure is that it reflects how much vapor is present above the liquid in the container, which relates to the tendency of the liquid to escape into the gas phase.

High vapor pressure means that a significant amount of molecules are escaping the liquid phase and entering the vapor phase, which can be very important in understanding fire behavior, as substances with high vapor pressures can ignite more easily and pose higher risks in a fire scenario.

The other options do not accurately capture what vapor pressure represents. It is not a direct measure of the amount of liquid present, nor does it necessarily indicate the temperature of a substance—though temperature does influence vapor pressure. It also does not provide a measure of the density of a liquid, which is a different physical property.