What is a quasi-static process?

In a thermodynamic process of uncontrolled change satisfying the equation $Q=W=0$,where $Q$ is heat supplied and $W$ is work done,the process is:

$A$ container of volume $1 \ m^3$ is divided into two equal compartments by a partition. One of these compartments contains an ideal gas at $300 \ K$. The other compartment is vacuum. The whole system is thermally isolated from its surroundings. The partition is removed and the gas expands to occupy the whole volume of the container. Its temperature now would be ..... $K$.

Which of the following processes is reversible?

Which of the following is not reversible?

$A$ container with insulating walls is divided into two equal parts by a partition fitted with a valve. One part is filled with an ideal gas at a pressure $P$ and temperature $T$,whereas the other part is completely evacuated. If the valve is suddenly opened,the pressure and temperature of the gas will be