Sodium hydroxide is prepared by the electrolysis of sodium chloride solution the electrodes used as cathode and anode are respectively

Options

A. mercury and platinum
B. platinum and mercury
C. mercury and carbon
D. carbon and mercury

Answer

To solve the question regarding the electrodes used in the electrolysis of sodium chloride solution for the preparation of sodium hydroxide, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electrolysis**:
- Electrolysis is a chemical process that uses electricity to drive a non-spontaneous reaction. In this case, we are focusing on the electrolysis of sodium chloride (NaCl) solution.

2. **Identifying the Cell Used**:
- The electrolysis of sodium chloride solution is typically carried out in a specific type of cell known as the Castner-Kellner cell.

3. **Identifying the Electrodes**:
- In the Castner-Kellner cell, the electrodes used are:
- **Cathode**: This is the electrode where reduction occurs. In this process, the cathode is made of **mercury**.
- **Anode**: This is the electrode where oxidation occurs. In this process, the anode is made of **carbon**.

4. **Reactions at the Electrodes**:
- At the cathode, sodium ions (Na⁺) gain electrons to form sodium amalgam:
\[ \text{Na}^+ + e^- \rightarrow \text{Na (amalgam)} \]
- At the anode, chloride ions (Cl⁻) lose electrons to form chlorine gas:
\[ 2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^- \]

5. **Formation of Sodium Hydroxide**:
- The sodium amalgam then reacts with water to produce sodium hydroxide (NaOH) and hydrogen gas (H₂):
\[ \text{Na (amalgam)} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2 + \text{Hg} \]

6. **Final Answer**:
- Therefore, the electrodes used in the electrolysis of sodium chloride solution are:
- **Cathode**: Mercury
- **Anode**: Carbon

### Conclusion:
The correct answer to the question is that the cathode is made of mercury and the anode is made of carbon.