Mass per unit volume; how tightly packed matter is.

• A. Volume
• B. Conductivity
• C. Density
• D. Solubility

Answer: (C)

Density is mass per unit volume, which is exactly a measure of how tightly packed matter is. If you have two objects that occupy the same amount of space, the one with more mass has more material in that space, so its density is higher. If an object has the same volume but less mass, its density is lower. That’s why density best captures the idea of “mass per unit volume” and how tightly packed the material is.

Volume describes how much space something takes up, not how much stuff is inside. Conductivity concerns how well a material can transfer heat or electricity. Solubility is about how a substance dissolves in a solvent. For example, a metal block and a wooden block of the same size might look similar, but the metal is denser because more mass fits into the same volume.