Which term describes the density comparison to water?

• A. Molar mass
• B. Viscosity
• C. Density relative to air
• D. Relative density

Answer: (D)

Relative density is the term that describes how dense a substance is compared with water. It’s the ratio of the substance’s density to the density of water (usually at 4°C), so it’s a unitless number that directly tells you buoyancy behavior. If the relative density is less than 1, the material will float on water; if it’s greater than 1, it will sink. This makes it especially useful in hazmat work for predicting how a liquid will behave in spills, during containment, and in environmental scenarios.

Molar mass is about how much matter is in a specific amount of substance, not how heavy it is relative to water. Viscosity measures how easily a substance flows, not its density. A density relative to air isn’t the standard way to compare density to water, whereas relative density (specific gravity to water) is the established term for that purpose.