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

• A. Specific gravity is the product of the density of a substance and the density of water.
• B. Specific gravity is the sum of the density of a substance and the density of water.
• C. Specific gravity is the ratio of the density of a substance to the density of water.
• D. Specific gravity is the difference between the density of a substance and the density of water.

Answer: (C)

Verified step by step guidance

1. Understand that specific gravity (SG) is a dimensionless quantity used to compare the density of a substance to the density of a reference substance, usually water at 4°C.
2. Recall the definition of density, which is mass per unit volume, expressed as \(\rho = \frac{m}{V}\), where \(\rho\) is density, \(m\) is mass, and \(V\) is volume.
3. Recognize that specific gravity is calculated by dividing the density of the substance by the density of water, which can be written as \(SG = \frac{\rho_{\text{substance}}}{\rho_{\text{water}}}\).
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 is not a product, sum, or difference of densities, but specifically the ratio of the density of a substance to the density of water.