The vapors given off by heated fuel oil are flammable, explosive, and __________.

Correct Answer: Option B — heavier than air

Petroleum vapors, including those from heated fuel oil, are significantly denser than air. This characteristic causes them to accumulate in low-lying areas, bilges, and pump rooms, creating persistent fire and explosion hazards. Proper ventilation and gas monitoring are required to prevent the dangerous pooling of these heavy, flammable vapors.