What does the term "vapor density" indicate about a chemical?

Vapor density is a crucial property in understanding how a chemical will behave in the atmosphere. Specifically, it refers to the density of a vapor compared to that of air. When a substance has a vapor density less than 1, it is typically lighter than air and will rise. Conversely, if the vapor density is greater than 1, the vapor is heavier than air and tends to settle to the ground. This property is important for assessing potential hazards and planning safety measures in hazardous material situations. Understanding whether vapors will rise or settle affects ventilation strategies and exposure risks for personnel.

The other options pertain to different properties of chemicals but do not directly relate to vapor density. Solubility in water, flammability at various temperatures, and toxicity levels are distinct chemical characteristics that would require separate assessments outside the scope of vapor density.