Which of the following is $NOT$ a reversible process?

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

$Assertion :$ In free expansion of an ideal gas,the entropy increases.
$Reason :$ Entropy increases in all natural processes.

If a cylinder containing a gas at high pressure explodes,the gas undergoes

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?

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