Which of the following is not reversible?

Write a short note on reversible and irreversible processes.

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

There is no change in internal energy of an ideal gas when it undergoes

Consider the given diagram. An ideal gas is contained in a chamber (left) of volume $V$ and is at an absolute temperature $T$. It is allowed to rush freely into the right chamber of volume $V$ which is initially vacuum. The whole system is thermally isolated. What will be the final temperature once the equilibrium has been attained?

What is a quasi-static process?