The condition for a reversible cyclic process is

Explanation:

, represents entropy in a cyclic process.

Generally, 

and  represents a cyclic integration of S and represented as 

 for any cycle.

Additional Information

As per Clausius Inequality

If  the cycle is reversible.

If  the cycle is irreversible.

If  the cycle is impossible.

Since entropy is a property, the cyclic integral of any property is zero