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 solve the question regarding the gas evolved at the anode during the preparation of NaOH in a Castner-Kellner cell, we can follow these steps:

### Step 1: Understand the Process
The Castner-Kellner cell is used for the electrolysis of sodium chloride (NaCl) solution to produce sodium hydroxide (NaOH).

**Hint:** Familiarize yourself with the electrolysis process and the specific reactions occurring in the Castner-Kellner cell.

### Step 2: Identify the Electrolysis Reactions
During electrolysis, two main reactions occur: one at the anode and one at the cathode.

- **At the Anode:** Chloride ions (Cl-) are oxidized to chlorine gas (Cl2).
- **At the Cathode:** Sodium ions (Na+) are reduced to form sodium metal (Na).

**Hint:** Remember that oxidation occurs at the anode and reduction occurs at the cathode.

### Step 3: Write the Half-Reaction at the Anode
The half-reaction at the anode can be represented as follows:
\[ 2Cl^- \rightarrow Cl_2 + 2e^- \]
This indicates that two chloride ions lose electrons to form one molecule of chlorine gas.

**Hint:** Pay attention to the stoichiometry of the reaction to understand how many moles of gas are produced.

### Step 4: Identify the Gas Evolved
From the half-reaction, we see that chlorine gas (Cl2) is produced at the anode.

**Hint:** Look for the specific gas mentioned in the question options.

### Step 5: Conclusion
Therefore, the gas evolved at the anode during the preparation of NaOH in the Castner-Kellner cell is chlorine gas (Cl2).

**Final Answer:** Cl2

### Summary of Steps:
1. Understand the electrolysis process in the Castner-Kellner cell.
2. Identify the reactions occurring at the anode and cathode.
3. Write the half-reaction for the anode.
4. Determine the gas produced.
5. Conclude with the answer.