Is the rusting of iron a reversible process? Why?

Which of the following is not reversible?

$A$ 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?

$A$ balloon filled with helium ($32^{\circ} C$ and $1.7 \; atm$) bursts. Immediately afterwards,the expansion of helium can be considered as:

Two cylinders $A$ and $B$ of equal capacity are connected to each other via a stop cock. Cylinder $A$ contains an ideal gas at standard temperature and pressure. Cylinder $B$ is completely evacuated. The entire system is thermally insulated. The stop cock is suddenly opened. The process is: