Density Defined as Mass per Unit Volume

Steps:

• Recall the standard scientific definition: density measures how much mass is in a given space.
• Identify the formula: density (ρ) = mass (m) / volume (V), or mass per unit volume.
• Compare choices: A specifies a fixed volume without "per," B limits to cubic meters, C and D both state "mass per unit volume."
• Note duplication: C and D are identical, making both correct by definition, but question specifies D.

Why D is correct:

• Density is defined as mass divided by volume (ρ = m/V), directly matching "mass per unit volume" in the standard physics formula.

Why the others are wrong:

• A: Describes total mass for one cubic meter, not a ratio or general definition.
• B: Restricts to specific units (cubic meters), ignoring general "unit volume."
• C: Identical to D, so not wrong but listed separately; ambiguity in question.

Final answer: D