Density can be described as which of the following, with the correct option located second?

• A. Ratio of mass to area
• B. Mass per unit volume
• C. Weight per unit volume
• D. Volume per unit mass

Answer: (B)

Density measures how much matter is packed into a given space. The standard description is mass per unit volume. It’s written as ρ = m/V, where m is mass and V is volume. This makes density an intrinsic property of a material: for a given substance at a specific temperature and pressure, its density stays the same regardless of how much you have. The units we typically use are kilograms per cubic meter (kg/m^3) or grams per cubic centimeter (g/cm^3).

Think of it as how tightly the material’s particles are packed. A substance with a high density has a lot of mass for each unit of volume; a substance with a low density has less mass in the same volume. This concept helps explain why objects sink or float and why different materials feel heavier or lighter when you hold them.

Why the other descriptions don’t fit as density: a ratio of mass to area would give mass per area, which describes surface density, not material density. If you used volume per mass, you’d be taking the reciprocal of density, which describes a different quantity. Weight per unit volume would involve gravity and would be a weight density, not mass density.