Specific gravity is defined as the weight of a substance compared to the weight of an equal volume of water at a given temperature.

Specific gravity is defined as the weight of a substance compared to the weight of an equal volume of water at a given temperature.

• A. The density of air at the same temperature.
• B. The ratio of vapor density to air density.
• C. The ratio of a liquid's boiling point to water's boiling point.
• D. Mass (weight) of a substance compared to the weight of an equal volume of water at a given temperature.

Answer: (D)

Specific gravity shows how dense a substance is compared with water for the same volume. It’s a ratio of densities, and since density is mass per unit volume, it can be viewed as the ratio of weights for equal volumes at the same temperature. That makes it a dimensionless number that tells you how heavy or light the substance is relative to water: if the value is greater than 1, the substance is heavier than water and tends to sink; if it’s less than 1, it’s lighter and may float. This definition uses water as the reference, which is why the statement describes the weight of a substance compared to the weight of an equal volume of water. The other ideas—the density of air, vapor density relative to air, or boiling-point ratios—don’t define specific gravity for liquids.

Specific gravity shows how dense a substance is compared with water for the same volume. It’s a ratio of densities, and since density is mass per unit volume, it can be viewed as the ratio of weights for equal volumes at the same temperature. That makes it a dimensionless number that tells you how heavy or light the substance is relative to water: if the value is greater than 1, the substance is heavier than water and tends to sink; if it’s less than 1, it’s lighter and may float. This definition uses water as the reference, which is why the statement describes the weight of a substance compared to the weight of an equal volume of water. The other ideas—the density of air, vapor density relative to air, or boiling-point ratios—don’t define specific gravity for liquids.