For the free expansion of a gas,which of the following is true?

Which of the following is $NOT$ a reversible 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:

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

Following are statements of a few processes taking place in nature:
$I$. Free expansion of a gas
$II$. The combustion of a mixture of petrol and air ignited by a spark
$III$. The leaking of gas from the kitchen cylinder
$IV$. The transfer of heat from one heated part of a liquid to the other colder part
Which amongst these processes are irreversible in nature?

$A$ 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 ..... $K$.