According to the kinetic molecular theory, which of the following objects contains molecules that are in constant motion?

• A. A perfectly still rock in space at 0 K
• B. A diamond at 0 K
• C. A solid metal at absolute zero (0 K)
• D. A block of ice at 0°C

Answer: (D)

Verified step by step guidance

1. Understand the kinetic molecular theory, which states that molecules are always in constant motion unless they are at absolute zero (0 K), where theoretically all molecular motion ceases.
2. Recognize that at 0 K (absolute zero), molecular motion stops completely, so objects like a perfectly still rock in space at 0 K, a diamond at 0 K, and a solid metal at 0 K have molecules that are not moving.
3. Note that a block of ice at 0°C is well above absolute zero, so its molecules have thermal energy and are vibrating or moving, consistent with the kinetic molecular theory.
4. Conclude that only the block of ice at 0°C contains molecules in constant motion because it is not at absolute zero and thus has molecular kinetic energy.
5. Therefore, the correct answer is the block of ice at 0°C, as it aligns with the principle that molecular motion occurs at temperatures above 0 K.