Which process is acceptable in nature: a reversible or an irreversible process?

$A$ container with rigid walls is covered with perfectly insulating material. The container is divided into two parts by a partition. One part contains a gas while the other is fully evacuated (vacuum). The partition is suddenly removed. The gas rushes to fill the entire volume and comes to equilibrium after a little time. If the gas is not ideal,then

$A$ perfect gas contained in a cylinder is kept in vacuum. If the cylinder suddenly bursts,then the temperature of the gas

When a gas in a vacuum chamber expands suddenly,which of the following is true?

$A$ 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 is not reversible?