Which is not a state function of a thermodynamic system?
Internal energy (U)
Free energy (G)
Enthalpy (H)
Work (W).

Options

A. Internal energy (U)
B. Free energy (G)
C. Enthalpy (H)
D. Work (W).

Explanation

To determine which of the given options is not a state function of a thermodynamic system, we need to understand the definitions of state functions and path functions.

### Step-by-Step Solution:

1. **Define State Functions**:
State functions are properties of a system that depend only on the current state of the system, regardless of how the system reached that state. Examples include internal energy (U), enthalpy (H), and free energy (G).

2. **Identify the Options**:
- **Internal Energy (U)**: This is a state function because it depends only on the initial and final states of the system.
- **Free Energy (G)**: This is also a state function. It depends on the initial and final states of the system.
- **Enthalpy (H)**: This is another state function that depends solely on the initial and final states of the system.
- **Work (W)**: Work is not a state function. It depends on the path taken to go from the initial state to the final state.

3. **Conclusion**:
Since internal energy, free energy, and enthalpy are all state functions, the only option that is not a state function is **Work (W)**.

### Final Answer:
**Work (W)** is not a state function of a thermodynamic system.

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