Which term matches the definition: 'The mass of a substance occupying a unit of volume'?

• A. Density
• B. Atomic Number
• C. Atomic Mass Number
• D. Compound

Answer: (A)

The concept being tested is how much matter is packed into a given space—that is, density. Density means mass per unit volume, so the phrase “The mass of a substance occupying a unit of volume” directly defines density. You get density by dividing the mass by the volume, with common units like grams per cubic centimeter (g/cm^3) for solids or kilograms per cubic meter (kg/m^3) for many practical applications.

Atomic number refers to the number of protons in an atom and identifies the element. Atomic mass number is the total count of protons and neutrons in an atom. A compound is a substance made from two or more elements chemically bonded together. These terms describe composition or identity, not how much matter fits into a space, which is why density is the correct match.