Which of the following processes is the best practical example of a reversible process?
(a) Slow adiabatic expansion of an ideal gas with an infinitesimal pressure difference from the surroundings.
(b) Slow isothermal expansion of an ideal gas with an infinitesimal pressure difference from the surroundings.
(c) Slow isothermal expansion of an ideal gas into a vacuum (zero external pressure).
(d) Melting of ice at 0∘C in a room maintained at 0.1∘C.