At absolute zero, which is equivalent to 0 Kelvin or approximately -273.15 degrees Celsius, the molecules in a gas would theoretically have no thermal energy. According to classical physics, at this temperature, all molecular motion would cease, and the gas would be in a state known as absolute rest.
However, in reality, achieving a temperature of absolute zero is not practically possible. This is due to the Heisenberg uncertainty principle, a fundamental principle in quantum mechanics, which states that the position and momentum of a particle cannot both be precisely determined simultaneously. As a consequence of this principle, even at absolute zero, particles would still possess some residual motion known as zero-point energy. This energy arises from quantum mechanical fluctuations and cannot be eliminated completely.
So, while the molecules in a gas would have minimal motion at temperatures close to absolute zero, they would still exhibit some residual vibrations due to quantum effects. This residual motion is a result of the uncertainty principle and is inherent to the nature of matter at the atomic and subatomic level.