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?

Free expansion of a gas is a spontaneous process where a gas expands into a vacuum, which cannot be reversed without external work, making it irreversible.

The combustion of a mixture of petrol and air is a chemical reaction that releases heat and changes the chemical composition permanently, making it an irreversible process.

The leaking of gas from a high-pressure cylinder to a lower-pressure environment is a spontaneous expansion, which is irreversible.

The transfer of heat from a hotter part to a colder part of a liquid occurs spontaneously due to a finite temperature difference. Heat cannot flow from cold to hot without external work, making this process irreversible.

Since all the given processes occur spontaneously in one direction and cannot be reversed without leaving a change in the surroundings, they are all irreversible in nature.

Answer: I, II, III and IV