A density measurement describes what property of a substance?

Density is defined as the mass of a substance divided by its volume, which means it quantifies how much matter is contained in a specific volume of that substance. This relationship is typically expressed in units such as grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³).

Measuring density allows for understanding how tightly packed the molecules of a material are. This property is crucial in various applications, particularly in fields like water treatment, where the density of different liquids can affect their behavior and interaction with one another.

In contrast, other options represent different physical properties. The hardness relates to a material's resistance to deformation or scratching. The volume of a liquid describes the amount of space it occupies, while the freezing temperature indicates the point at which a substance changes from liquid to solid. Each of these properties is important but essentially different from what density represents.