Which of the following is a state function?

Options

A. q
B. Work
C. q + w
D. All of these

Answer

To determine which of the following is a state function, we first need to understand the definitions of state functions and path functions.

### Step-by-Step Solution:

1. **Define State Functions and Path Functions**:
- State functions are properties that depend only on the current state of the system, regardless of how that state was reached. Examples include internal energy, enthalpy, entropy, and pressure.
- Path functions, on the other hand, depend on the specific path taken to reach a particular state. Examples include heat (Q) and work (W).

2. **Identify the Options**:
- If the question provides multiple options (e.g., internal energy, heat, work, enthalpy), we need to categorize each option as either a state function or a path function.

3. **Classify Each Option**:
- **Internal Energy (U)**: This is a state function because it depends only on the initial and final states of the system.
- **Enthalpy (H)**: This is also a state function for the same reason as internal energy.
- **Entropy (S)**: This is a state function as well, as it depends only on the state of the system.
- **Heat (Q)**: This is a path function because it depends on the process taken to transfer energy.
- **Work (W)**: This is also a path function since the work done can vary depending on the path taken.

4. **Conclusion**:
- Based on the classifications, the state functions among the options are internal energy, enthalpy, and entropy. The path functions are heat and work.

### Final Answer:
The state functions are **internal energy (U)**, **enthalpy (H)**, and **entropy (S)**.