Which of the following has been universally accepted as a reference electrode at all temperature and has been assigned a value of zero volt?

Options

A. platinum electrode
B. copper electrode
C. graphite electrode
D. standard hydrogen electrode.

Answer

To solve the question regarding which electrode has been universally accepted as a reference electrode at all temperatures and assigned a value of zero volts, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Reference Electrodes**:
- A reference electrode is a stable and known electrode potential against which the potential of other electrodes can be measured.

2. **Identifying the Options**:
- The options provided are:
- A) Platinum Electrode
- B) Copper Electrode
- C) Graphite Electrode
- D) Standard Hydrogen Electrode

3. **Evaluating Each Option**:
- **A) Platinum Electrode**: While platinum is used in various electrochemical applications, it is not a reference electrode with a defined potential of zero volts.
- **B) Copper Electrode**: The copper electrode does not have a universally accepted potential of zero volts and is not used as a primary reference electrode.
- **C) Graphite Electrode**: Graphite can be used in electrochemical cells but is not a standard reference electrode with a defined potential.
- **D) Standard Hydrogen Electrode (SHE)**: The Standard Hydrogen Electrode is universally accepted as a reference electrode. It is defined to have a potential of exactly zero volts at all temperatures.

4. **Conclusion**:
- Based on the evaluation, the Standard Hydrogen Electrode (SHE) is the correct answer as it is the primary standard electrode and has been assigned a value of zero volts.

### Final Answer:
The correct answer is **D) Standard Hydrogen Electrode**.

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