What is a quasi-static process?

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

$A$ thermally insulated container is divided into two parts by a screen. In one part,an ideal gas is filled at pressure $P$ and temperature $T$. The second part is a vacuum. If a small hole is now created in the screen,the temperature of the gas will:

Which of the following processes is reversible?

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

$A$ 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?