Explanation:
In thermodynamics, there are properties and processes. Properties are the state variables that depend only on the current state of the system and not on the process used to achieve that state. Whereas, processes are the ways in which a system can change from one state to another state.

a)pdv and b)vdp are the expressions of the first law of thermodynamics, which relates the changes in internal energy of a system to the work done on the system and the heat added to the system.

c)cyclic pdv and d)cyclic vdp are the expressions of cyclic processes, which are processes that start and end at the same state, and have a net change of zero in all the state variables. Cyclic processes are important because they allow the system to perform work without a net change in any state variable.

Therefore, the answer is option 'C', which represents a cyclic process and not a property of the system. The cyclic process involves a closed loop, which starts and ends at the same state, and therefore, the net change in volume is zero. As a result, cyclic pdv is also zero and does not represent a property of the system.

Conclusion:
In thermodynamics, it is important to distinguish between properties and processes. Properties are the state variables that depend only on the current state of the system and not on the process used to achieve that state. Processes are the ways in which a system can change from one state to another state. Cyclic processes are important because they allow the system to perform work without a net change in any state variable.