Which of the following state function is not zero at standard state :-

Options

A. Enthalpy
B. Entropy
C. Free energy
D. None

Answer

To solve the question "Which of the following state function is not zero at standard state?", we will analyze the properties of various state functions, particularly focusing on entropy, enthalpy, and Gibbs free energy.

### Step-by-Step Solution:

1. **Understanding State Functions**:
- State functions are properties that depend only on the state of the system, not on how it reached that state. Examples include internal energy, enthalpy, entropy, and Gibbs free energy.

2. **Identifying Standard State**:
- The standard state of a substance is defined as its most stable form at 1 bar pressure and a specified temperature (usually 25°C or 298 K).

3. **Analyzing Each State Function**:
- **Entropy (S)**: Entropy is a measure of the randomness or disorder of a system. At absolute zero (0 K), the entropy of a perfect crystal is zero, but at standard state (25°C), the entropy of most substances is greater than zero due to the inherent disorder in the system.
- **Enthalpy (H)**: Enthalpy can be defined for a reaction or a system. The standard enthalpy of formation for elements in their standard state is defined as zero. Therefore, enthalpy can be zero at standard state for elements.
- **Gibbs Free Energy (G)**: Similar to enthalpy, the standard Gibbs free energy of formation for elements in their standard state is also defined as zero. Thus, Gibbs free energy can also be zero at standard state for elements.

4. **Conclusion**:
- Among the state functions discussed, only entropy is not zero at standard state. Therefore, the answer to the question is that entropy is the state function that is not zero at standard state.

### Final Answer:
The state function that is not zero at standard state is **Entropy**.

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