Which statement correctly defines specific gravity?

Which statement correctly defines specific gravity?

• A. The ratio of mass to volume of the substance.
• B. The ratio of the density of air to the density of the substance.
• C. The inverse of the density of the substance.
• D. The ratio of the density of the substance to the density of water at the same temperature.

Answer: (D)

Specific gravity is a dimensionless measure that compares how dense a substance is to water. It is defined as the density of the substance divided by the density of water at the same temperature. Because the same units cancel, you get a pure number that lets you compare materials quickly. For example, if water at the measurement temperature has a density of 1.0 g/cm^3, a substance with density 1.2 g/cm^3 has a specific gravity of about 1.2, while a density of 0.8 g/cm^3 gives about 0.8. The temperature must match because water’s density changes with temperature, and that keeps the comparison meaningful. The other ideas describe density itself, or other quantities like inverse density (specific volume) or a ratio to air, but they do not define specific gravity. The statement that fits is the ratio of the substance’s density to water’s density at the same temperature.

Specific gravity is a dimensionless measure that compares how dense a substance is to water. It is defined as the density of the substance divided by the density of water at the same temperature. Because the same units cancel, you get a pure number that lets you compare materials quickly. For example, if water at the measurement temperature has a density of 1.0 g/cm^3, a substance with density 1.2 g/cm^3 has a specific gravity of about 1.2, while a density of 0.8 g/cm^3 gives about 0.8. The temperature must match because water’s density changes with temperature, and that keeps the comparison meaningful. The other ideas describe density itself, or other quantities like inverse density (specific volume) or a ratio to air, but they do not define specific gravity. The statement that fits is the ratio of the substance’s density to water’s density at the same temperature.