When NaOH is prepared in Castner-Kellner cell,the gas evolved at the anode is

Options

A. `O_2`
B. `O_3`
C. `Cl_2`
D. HCl

Answer

To determine the gas evolved at the anode when sodium hydroxide is prepared in a Castner-Kellner cell, we need to consider the process of electrolysis of aqueous sodium chloride (NaCl).

**Step-by-Step Solution:**

1. **Understanding the Electrolysis Process:**
- The Castner-Kellner cell is used for the electrolysis of brine (aqueous sodium chloride).
- During electrolysis, two electrodes are involved: the anode (positive electrode) and the cathode (negative electrode).

2. **Identifying Reactions at the Electrodes:**
- At the cathode, reduction occurs, where sodium ions (Na⁺) gain electrons to form sodium metal (Na).
- At the anode, oxidation occurs, where chloride ions (Cl⁻) lose electrons.

3. **Anode Reaction:**
- The oxidation of chloride ions can be represented by the following half-reaction:
\[ 2 \text{Cl}^- \rightarrow \text{Cl}_2(g) + 2 \text{e}^- \]
- This reaction indicates that two chloride ions lose electrons to form chlorine gas (Cl₂).

4. **Conclusion:**
- Therefore, the gas evolved at the anode during the electrolysis of aqueous sodium chloride in the Castner-Kellner cell is chlorine gas (Cl₂).

**Final Answer:**
The gas evolved at the anode is chlorine gas (Cl₂).

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