Which of the following best describes the concept of density and what it reveals about a substance?

• A. Density is the ratio of a substance's temperature to its pressure; it shows how hot the substance is.
• B. Density is the amount of energy stored in a substance; it tells you how reactive the substance is.
• C. Density is the total mass of a substance; it tells you how much of the substance is present.
• D. Density is the mass per unit volume of a substance; it indicates how tightly matter is packed within the substance.

Answer: (D)

Verified step by step guidance

1. Understand that density is a physical property of matter that relates mass and volume.
2. Recall the formula for density: \(\text{Density} = \frac{\text{Mass}}{\text{Volume}}\).
3. Recognize that density tells us how much mass is contained in a given volume, which reflects how tightly the matter is packed.
4. Compare the given options to see which one correctly defines density and its significance.
5. Identify that the correct description is: Density is the mass per unit volume of a substance; it indicates how tightly matter is packed within the substance.