What does vapor pressure indicate about a substance?

Vapor pressure is a crucial indicator of a substance's volatility, which refers to how readily it transitions from a liquid to a gaseous state. It represents the pressure exerted by the vapor of a substance when it is in equilibrium with its liquid (or solid) phase at a given temperature. Substances with high vapor pressures at room temperature are considered volatile; they evaporate more easily compared to those with lower vapor pressures.

Understanding vapor pressure helps chemists anticipate how substances will behave under different conditions, such as temperature changes, which can significantly influence the evaporation rate. This concept is particularly important in various applications, including distillation, formulation of products, and assessing environmental impacts of volatile compounds.

The other options do not accurately relate to vapor pressure. For instance, cloudiness pertains to the presence of suspended particles, solubility is about how well a substance dissolves, and density relates to mass and volume relationships, rather than the specific behavior associated with evaporation and vapor formation.