Its density to the density of water.
Explanation
Relative density, often referred to as specific gravity, is a comparative measure used to determine the heaviness of a substance relative to a standard reference.
- Definition: Relative density is defined as the ratio of the density of a substance to the density of water (typically at 4°C, where water is most dense).
- Mathematical Expression:
Relative Density = $\frac{\text{Density of Substance}}{\text{Density of Water}}$ - Nature of Quantity: Since it is a ratio of two identical physical quantities (density over density), it is a dimensionless quantity and possesses no unit.
Analysis of Incorrect Options:
- Its mass to its volume.: The ratio of mass to volume defines Absolute Density ($\rho = \frac{m}{v}$), not relative density.
- Its weight to its mass.: The ratio of weight to mass corresponds to the acceleration due to gravity ($g = \frac{W}{m}$).
- Its volume to the volume of water.: The ratio of a substance's volume to the volume of water does not define a standard physical property.
Key Takeaway: Relative density is a unitless ratio. A relative density greater than 1 indicates the substance is denser than water and will sink, whereas a value less than 1 indicates it will float.