Gas at absolute zero According to Charles's Law, the volume of gas is proportional to temperate at constant pressure. So, the volume of a gas decreases as temperature decreases. 
Then, in theory, as the temperature approaches absolute Kelvin when motion in all matter ceases, the volume of gas must be pretty close to 0.
How would you describe this state of gas? Is it gas at all? How would this gas be different from a solid?
 A: The matter which was once in a gaseous state is no longer in that state as temperatures approach absolute zero. As you keep decreasing the temperature, quantum mechanical effects become more and more dominant. You have to scrap the classical understanding of the behavior of gasses. They simply don't apply at such low temperatures. That being said, Charles' law's claim that the matter (which once had finite volume) has zero volume at absolute zero is absolutely false.
Not just that, motion does not cease nor is all the energy of the system taken away. A system at absolute zero still possesses some energy known as zero-point energy.
Are the particles motionless? Saying so is like throwing a tomato at Heisenberg's face.
The Heisenberg's uncertainty principle states that the produce of the uncertainties in the particle's momentum and position must be greater than a specific value.
$$\Delta p \Delta x \ge \frac{h}{4\pi}$$
where $p$ is the particle's momentum, $x$ is the particle's position and $h$ is the Planck's constant.
Therefore, the particles must have some jitteriness. If the particles were motionless then the position, as well as momentum, would be zero which is a direct violation of the uncertainty principle.
