The correct answer is option 'c) Ericsson cycle'. The Ericsson cycle is a thermodynamic cycle that consists of two reversible isotherms and two reversible isobars. Let's break down the components of the Ericsson cycle to understand why this is the correct answer.

1. ISOTHERM 1:
The cycle starts with an isothermal compression process (Isobaric Heat Addition) where heat is added to the system at constant temperature. During this process, the working fluid (typically a gas) is compressed while maintaining a constant temperature. This is represented by a horizontal line on a pressure-volume (PV) diagram.

2. ISOBAR 1:
After the isothermal compression, the working fluid undergoes an isobaric heat addition process. In this process, the working fluid is heated at constant pressure. The heat transfer causes an increase in the volume of the working fluid while maintaining a constant pressure. This process is represented by a vertical line on a PV diagram.

3. ISOTHERM 2:
Following the isobaric heat addition process, the working fluid undergoes an isothermal expansion process (Isobaric Heat Rejection) where heat is rejected from the system at constant temperature. During this process, the working fluid expands while maintaining a constant temperature. This is represented by another horizontal line on a PV diagram.

4. ISOBAR 2:
Finally, after the isothermal expansion, the working fluid undergoes an isobaric heat rejection process. In this process, the working fluid is cooled at constant pressure. The heat transfer causes a decrease in the volume of the working fluid while maintaining a constant pressure. This process is represented by another vertical line on a PV diagram.

By combining these four processes, the Ericsson cycle completes a full thermodynamic cycle. The cycle can be represented on a PV diagram as a rectangle or a closed loop. The two reversible isotherms represent the constant temperature processes, and the two reversible isobars represent the constant pressure processes.

The Ericsson cycle is commonly used in certain types of engines, such as the Ericsson engine, which is an external combustion engine. It is also used in some refrigeration cycles.