What does specific gravity compare?

Specific gravity is a dimensionless quantity that specifically compares the density of a substance to the density of a reference substance, typically water, for liquids and solids, or air for gases. In this case, the correct answer identifies that specific gravity compares the density of a mineral to an equal volume of water.

When determining specific gravity, you essentially measure how much denser the mineral is than water. If a mineral has a specific gravity greater than 1, it is denser than water and will sink, while if it is less than 1, it will float. This comparison is crucial in fields like geology and material science, as it provides a way to evaluate materials in relation to water, which is a common reference point.

The other options refer to different concepts not associated with specific gravity. For example, comparing weight to size does not convey density or buoyancy properties, while temperature and viscosity are distinct physical properties not related to density. Lastly, volume and mass can pertain to gas measurements but do not specifically relate to the concept of specific gravity.