What does vapour density compare?

Vapor density is a measure that compares the weight of a gas to an equal volume of air. This relationship is important for understanding how gases will behave in different environments, particularly in confined spaces. For instance, if a gas has a vapor density greater than 1, it is heavier than air and will tend to accumulate in low-lying areas, which could pose a safety risk during rescue operations. Understanding vapor density helps in assessing potential hazards, ensuring adequate ventilation, and planning for safe rescue operations in confined spaces.

While other choices present comparisons relevant to physical states and properties, they do not accurately describe vapor density in the context of gases and air, which is critical for evaluating the behavior of gases in scenarios involving confined spaces.