When a substance reaches absolute zero temperature, what happens to its molecules?

• A. They stop moving completely.
• B. They undergo chemical reactions spontaneously.
• C. They gain kinetic energy.
• D. They vibrate rapidly.

Answer: (A)

Verified step by step guidance

1. Understand the concept of absolute zero, which is defined as 0 Kelvin (or -273.15°C), the theoretical temperature at which a system has minimum thermal energy.
2. Recall that temperature is a measure of the average kinetic energy of molecules; as temperature decreases, molecular motion slows down.
3. At absolute zero, the kinetic energy of molecules reaches its minimum possible value, meaning molecular motion essentially ceases.
4. Recognize that molecules do not undergo chemical reactions spontaneously just because the temperature is at absolute zero; chemical reactions generally require energy input.
5. Conclude that at absolute zero, molecules stop moving completely, meaning they have no kinetic energy and do not vibrate or move.