Concentration of mass in a volume.

• A. Density
• B. Pressure
• C. Distance
• D. Temperature

Answer: (A)

Concentration of mass in a volume is described by density. Density is defined as mass per unit volume, showing how tightly matter is packed in a space. If you keep the mass the same but make the volume smaller, density increases; if you increase the volume with the same mass, density decreases. Density is an intensive property, meaning it depends on how the material is arranged in space, not on how much material you have overall. For example, a metal block and a wood block of the same size have different densities because the metal packs more mass into the same volume. Pressure, distance, and temperature relate to other physical concepts: pressure involves force per area, distance is about separation in space, and temperature reflects energy and motion; while temperature and density can influence each other through expansion or contraction, the direct measure of how much mass is in a given volume is density.