What happens to molecular motion at absolute zero?

At absolute zero, which is 0 Kelvin or -273.15 degrees Celsius, molecular motion theoretically reaches its lowest possible energy state. According to the third law of thermodynamics, at absolute zero, the entropy of a perfect crystal is exactly zero, suggesting that the atoms of the substance would be in their ground state and would have minimal vibrational motion.

While quantum mechanics indicates that atoms will still have some residual motion due to zero-point energy, the concept of complete cessation of molecular motion is widely accepted as the defining characteristic of absolute zero in classical terms. This reflects an ideal state where thermal energy is absent, and molecules exhibit no kinetic energy, thus effectively leading to the conclusion that molecular motion ceases.

This understanding aligns with the principles of thermodynamics and quantum mechanics, providing a foundation for why the correct choice emphasizes the cessation of motion at this extreme condition.