Is the rusting of iron a reversible process? Why?

What is an irreversible process and what is a reversible process?

Two cylinders $A$ and $B$ of equal capacity are connected to each other via a stopcock. $A$ contains a gas at standard temperature and pressure. $B$ is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. Answer the following :
$(a)$ What is the final pressure of the gas in $A$ and $B$?
$(b)$ What is the change in internal energy of the gas?
$(c)$ What is the change in the temperature of the gas?
$(d)$ Do the intermediate states of the system (before settling to the final equilibrium state) lie on its $P-V-T$ surface?

$A$ closed container is fully insulated from the outside. One half of it is filled with an ideal gas $X$ separated by a plate $P$ from the other half $Y$,which contains a vacuum as shown in the figure. When $P$ is removed,$X$ expands into $Y$. Which of the following statements is correct?

In case of free expansion, which one of the following statements is $\underline{\text{WRONG}}$?

$Assertion :$ Reversible systems are difficult to find in the real world.
$Reason :$ Most processes are dissipative in nature.