Molten `NaCl` is electrolyzed in a cell called
(a)Downs cell
(b)Castner cell
(c)Kellner cell
(d)All of these

Options

A. Downs cell
B. Castner cell
C. Kellner cell
D. All of these

Explanation

To solve the question regarding the electrolysis of molten NaCl, we will analyze each of the options provided:

### Step 1: Understand the Electrolysis of Molten NaCl
When molten sodium chloride (NaCl) is subjected to electrolysis, it dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻). The electrolysis process involves the movement of these ions towards the electrodes where they undergo reduction and oxidation.

### Step 2: Identify the Cell Types
1. **Downs Cell**: This cell is specifically designed for the electrolysis of molten NaCl. In this cell, sodium is produced at the cathode (negative electrode) and chlorine gas is produced at the anode (positive electrode).

2. **Castner Cell**: This cell is used for the production of sodium hydroxide (NaOH) from a saturated solution of NaCl. Although it utilizes NaCl, it is not specifically for molten NaCl but rather for a solution.

3. **Kellner Cell**: Similar to the Castner cell, the Kellner cell is also used for the production of sodium hydroxide from sodium chloride solution, not specifically molten NaCl.

### Step 3: Analyze the Options
- **(a) Downs cell**: Correct, as it is specifically used for the electrolysis of molten NaCl.
- **(b) Castner cell**: While it involves NaCl, it is not for molten NaCl but rather for a solution.
- **(c) Kellner cell**: Same as the Castner cell; it is not specifically for molten NaCl.
- **(d) All of these**: This option suggests that all the mentioned cells are used for the electrolysis of molten NaCl, which is incorrect because only the Downs cell is specifically for molten NaCl.

### Conclusion
The correct answer is **(a) Downs cell**.