Question

At which temperature does the motion of atoms and molecules stop?

Answer 1

Technically this would never occur, even at zero degrees Kelvin (-273 degrees C). The laws of quantum physics prevents any object from being completely still, because then you would know its position precisely, which is not possible. Instead, every object has a minimum amount of energy, which translates to motion for molecules. No matter how much you cool a gas down, there is a minimum amount of energy in motion that prevents you from knowing a gas molecules position precisely. This energy from minimum allowable motion is called "zero point energy."

Answer 2

Technically​this will not happen and is impossible