Which of the following statements is TRUE? O Molecules in a gas all move in different random directions but their speeds are all the same. O Liquid water can only exist on the surface of planets when there is an atmosphere. O At equilibrium, when considering a liquid and its vapour in a closed container, the pressure of the vapour increases when the volume of the container is reduced at constant temperature. O The density of a substance always decreases with increasing temperature. Two objects must be in physical contact to be in thermal equilibrium.