The vessel used for electric decomposition-

Options

A. Barometer
B. Ammeter
C. Voltmeter
D. Calorimeter

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the vessel used for electric decomposition. Electric decomposition refers to the process of breaking down a substance into its components using electric current.

2. **Identifying the Options**: The options given are barometer, ammeter, voltmeter, and calorimeter. We need to determine which of these is related to electric decomposition.

3. **Analyzing Each Option**:
- **Barometer**: This instrument measures atmospheric pressure and is not related to electric decomposition.
- **Ammeter**: This device measures the current flowing through a circuit but does not specifically relate to the vessel used for electric decomposition.
- **Voltmeter**: This instrument measures the electrical potential difference (voltage) between two points in a circuit. It is often used in experiments involving electric decomposition to monitor the voltage applied.
- **Calorimeter**: This device is used to measure the heat of chemical reactions or physical changes and is not directly related to electric decomposition.

4. **Conclusion**: The voltmeter is the most relevant instrument in the context of electric decomposition as it helps in measuring the voltage required for the process.

5. **Final Answer**: The vessel used for electric decomposition is a **voltmeter**.

---