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 functions is not zero at standard state?", we will analyze the options provided (A, B, C, D) based on the properties of state functions at standard conditions.

### 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 got there. Common state functions include enthalpy (H), entropy (S), and Gibbs free energy (G).

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

3. **Analyzing Each Option**:
- **Option A**: Enthalpy (ΔH) can be zero for elements in their standard state. Therefore, this option can be zero.
- **Option B**: Entropy (ΔS) is a measure of disorder. For a perfect crystal at absolute zero, entropy is zero, but at standard state (25°C), the entropy of substances is generally not zero. Thus, this option is likely not zero.
- **Option C**: Gibbs free energy (ΔG) can also be zero at equilibrium conditions, so this option can be zero.
- **Option D**: Another state function that can be zero under certain conditions, but we need to focus on the specific functions mentioned.

4. **Conclusion**:
- Among the options analyzed, entropy (ΔS) is the state function that is not zero at standard state conditions. Therefore, the correct answer is **Option B**.

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