In thermodynamics, a process is called reversible when
surroundings and system change into each other
there is no boundary between system and surroundings
the surrounding are always in equilibrium with the system
the system changes into the surroundings spontaneously
The correct option is D the surrounding are always in equilibrium with the system
A reversible process is a process that can be reversed by means of infinitesimal changes in some property of the system. Due to these infinitesimal changes, the system is in thermodynamic equilibrium with the surroundings throughout the entire process.