Among the following the irreversible process is
A. Free expansion of gas
B. Extension or compression of spring
C. Motion of an object on a perfectly frictionless surface
D. All of them

Hint: To answer this question we will use the definitions of irreversible and reversible processes and along with the examples. We know that, when the system returns to the initial state after many processes it is called a reversible process. Irreversible processes are just opposite to reversible processes. Fast and sudden processes are usually considered as irreversible.

Complete answer:
When the system returns to the initial state after many processes it is called a reversible process. Slow adiabatic compression or expansion of gases, slow isothermal expansion, slow isothermal compression, motion of an object on a frictionless surface, electrolysis etc are examples of reversible processes.

Irreversible processes are processes in which the system and surroundings do not return to its initial state. The motion of solids under friction, fast process, mixing of two different substances, heat transfer etc comes under the category of irreversible process.

Free expansion of gas happens when expansion occurs in vacuum. Work done during free expansion of gases is zero. In free expansion of gases, it is unable to define pressure, temperature, volume at all times. We can’t reverse the process at any time so it is an irreversible process.

Extension or compression of spring is reversible since it can be returned to its initial state at any time. Motion in a frictionless plane is also reversible since no extra energy is released.

Therefore, the answer is option (A)

Additional Information
When the system returns to the initial state after many processes it is called a reversible process. Slow adiabatic compression or expansion of gases, slow isothermal expansion, slow isothermal compression, motion of an object on a frictionless surface, electrolysis etc are examples of reversible processes.

Note: Free expansion is also called Joule expansion. This process is not quasi-static. That is the system does not attain equilibrium at any moment. But isothermal expansion or compression of gases are reversible.