Which property helps predict whether a liquid will float on water during a spill?

• A. Specific gravity
• B. Vapor pressure
• C. Flash point
• D. Boiling point

Answer: (A)

Floating on water is determined by how dense the liquid is relative to water. This is captured by specific gravity, which compares the liquid’s density to water’s density. If the specific gravity is less than 1, the liquid is lighter than water and will ride on the surface; if it’s greater than 1, it will sink. That direct link between density and buoyancy is why this property is the best predictor for whether a liquid will float during a spill.

Vapor pressure, flash point, and boiling point describe volatility and flammability, not whether a liquid will float. A liquid can be highly volatile or have a low flash point and still sink or float depending on its density relative to water.