What is the vapor density of air?

• A. 0.95
• B. 1.0
• C. 0.8
• D. 1.2

Answer: (B)

Vapor density compares how heavy a gas’s vapor is to the same amount of air, with air defined as the reference value of 1.0. Since air is the standard, its vapor density is 1.0.

This matters in safety: gases with density greater than 1.0 tend to linger close to the ground, while gases with density less than 1.0 rise toward the ceiling. For context, methane has a vapor density around 0.6 (lighter than air) and propane around 1.5 (heavier than air).

Therefore, the correct value for the vapor density of air is 1.0.