How is vapor density measured?

Vapor density is defined as the mass of a given volume of vapor compared to the mass of an equal volume of dry air at the same temperature and pressure. This means that it assesses how heavy a vapor is relative to dry air, which is crucial in fire dynamics and emergency response. When a vapor has a vapor density greater than 1, it is heavier than air and will tend to settle in lower areas, which can be hazardous in confined spaces as it may lead to the accumulation of flammable or toxic gases.

The other options do not accurately describe how vapor density is determined. Comparing the weight of vapor to the weight of a liquid doesn't provide useful information about the vapor's behavior in the atmosphere since liquids and vapors behave differently. Measuring the volume of gases produced offers data about the amount of vapor generated, but not about its density compared to air. Calculating combustibility assesses whether a compound can catch fire, but does not involve measuring its density at all. Thus, the correct method for measuring vapor density is through a comparison with dry air.