What is the value of the volume of an ideal gas at absolute zero temperature?

What is Boltzmann's constant?

An open container contains $x$ moles of gas at $T$ $K$. If the temperature is tripled,then the amount of gas that exits the container is:

$12\,g$ of gas occupies a volume of $4\times 10^{-3}\,m^3$ at a temperature of $7\,^oC$. After the gas is heated at constant pressure,its density becomes $6\times 10^{-4}\,g/cc$. Find the temperature $T$ (in $K$) to which the gas was heated.

At a temperature $T \ K$,the pressure of $4.0 \ g$ argon in a bulb is $p$. The bulb is put in a bath having a temperature higher by $50 \ K$ than the first one. $0.8 \ g$ of argon gas had to be removed to maintain the original pressure. The temperature $T$ is equal to ..... $K$.

The expansion of unit mass of a perfect gas at constant pressure is shown in the diagram. Here