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

Which of the following is not reversible?

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

Which of the following is an irreversible process?

$A$ container with rigid walls is covered with perfectly insulating material. The container is divided into two parts by a partition. One part contains a gas while the other is fully evacuated (vacuum). The partition is suddenly removed. The gas rushes to fill the entire volume and comes to equilibrium after a little time. If the gas is not ideal,then

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?