What is the definition of specific gravity?

Specific gravity is defined as the ratio of a material's density to the density of water at a specified temperature. This property is dimensionless, which means it is expressed as a numerical value without units. When determining specific gravity, the density of the substance is compared to that of water, typically at 4°C, where water reaches its maximum density.

By using this definition, specific gravity provides important insights into how a material will behave in various environments. For instance, materials with a specific gravity less than 1 will float in water, while those with a specific gravity greater than 1 will sink.

The other choices do not accurately describe specific gravity. The first option incorrectly relates mass to air rather than to water, which is crucial for defining specific gravity. The third choice confuses the concepts of volume and weight, and doesn't reference the comparative aspect of water. Lastly, while the fourth choice mentions weight and water, it introduces an unnecessary complexity by discussing weight rather than density, which is foundational to the concept of specific gravity.