What is the definition of specific gravity?

• A. The mass per unit volume of a substance
• B. The ratio of a substance's density to the density of water
• C. The temperature at which a substance boils
• D. The color of a substance compared to water

Answer: (B)

Specific gravity is a dimensionless measure of how dense a substance is compared with water. It’s defined as the density of the substance divided by the density of water (usually taken at 4°C). Because water’s density at that temperature is about 1 g/cm³, the specific gravity effectively tells you how many times denser the substance is than water. If the result is less than 1, the material is lighter than water and tends to float; if it’s greater than 1, it’s heavier than water and tends to sink. This concept is distinct from density itself, which has units of mass per volume, and from properties like boiling point or color, which are unrelated to the ratio.