Which two quantities must be known to calculate the density of a sample of matter?

• A. Mass and volume
• B. Molar mass and atomic number
• C. Temperature and pressure
• D. Length and width

Answer: (A)

Verified step by step guidance

1. Recall the definition of density, which is the mass of a substance divided by its volume. The formula is given by \(\text{Density} = \frac{\text{Mass}}{\text{Volume}}\).
2. Understand that to calculate density, you need to know the amount of matter present (mass) and the space it occupies (volume).
3. Recognize that molar mass and atomic number relate to the identity and amount of atoms but do not directly give density without volume information.
4. Note that temperature and pressure can affect density but are not the quantities directly used in the density calculation.
5. Length and width alone are dimensions but insufficient to find volume unless combined with height or depth, so they are not enough to calculate density.