Define absolute temperature.

(N/A) The average kinetic energy of one molecule of an ideal gas is given by the relation: $\langle \frac{1}{2} m v^{2} \rangle = \frac{3}{2} k_{B} T$.
Here,$k_{B}$ is the Boltzmann constant,$T$ is the absolute temperature,$m$ is the mass of the molecule,and $v$ is the speed of the gas molecule.
If $T = 0$,then $\langle \frac{1}{2} m v^{2} \rangle = 0$,which implies $\langle v^{2} \rangle = 0$,and consequently,the root-mean-square speed $v_{rms} = \sqrt{\langle v^{2} \rangle} = 0$.
Therefore,absolute temperature is defined as the temperature at which the root-mean-square speed $(v_{rms})$ of gas molecules becomes zero.
Using the relation $v_{rms} = \sqrt{\frac{3P}{\rho}}$,where $P$ is pressure and $\rho$ is density,we can see that at $T = 0$,the pressure $P$ must also be zero.