Which of the following best describes specific gravity and its relationship to density?

• A. Specific gravity is the absolute density of a substance measured in g/cm^3.
• B. Specific gravity is the difference between the density of a substance and the density of water.
• C. Specific gravity is the sum of the densities of a substance and water.
• D. Specific gravity is the ratio of the density of a substance to the density of water at a specified temperature.

Answer: (D)

Verified step by step guidance

1. Understand that specific gravity is a dimensionless quantity that compares the density of a substance to the density of a reference substance, usually water at 4°C.
2. Recall that density is defined as mass per unit volume, typically expressed as \(\rho = \frac{m}{V}\) with units like g/cm\(^3\).
3. Recognize that specific gravity is calculated by taking the ratio of the density of the substance (\(\rho_{\text{substance}}\)) to the density of water (\(\rho_{\text{water}}\)), which can be written as \(\text{Specific Gravity} = \frac{\rho_{\text{substance}}}{\rho_{\text{water}}}\).
4. Note that because specific gravity is a ratio of two densities with the same units, it has no units itself (dimensionless).
5. Conclude that specific gravity does not represent an absolute density value, nor is it a difference or sum of densities, but rather a ratio comparing the density of a substance to that of water.