In a closed space, vapors with a vapor density less than one will:

• A. rise and concentrate near the ceiling.
• B. rise and concentrate near the floor.
• C. mix evenly with air.
• D. rise and concentrate near the ceiling.

Answer: (D)

Vapors that are lighter than air will rise in a closed space because they are less dense than the surrounding air. As they ascend, buoyancy pushes them toward the highest point, so they tend to accumulate near the ceiling rather than staying mixed or pooling at the bottom. This stratification means the vapor forms a concentrated layer at the top, not a uniform mix with air or a buildup on the floor.