Which one of the following is true in electrolytic refining ?

Options

A. Impure metal is made cathode
B. Impure metal is made anode
C. Impure metal is made cathode and pure metal as anode
D. Both electrodes must be of pure metal.

Explanation

### Step-by-Step Solution:

1. **Understanding Electrolytic Refining**:
- Electrolytic refining is a process used to purify metals. It involves the use of an electrolytic cell where an impure metal is used as the anode and a pure metal is deposited at the cathode.

2. **Identifying the Electrodes**:
- In the electrolytic cell, the anode is where oxidation occurs, and the cathode is where reduction takes place. The impure metal (e.g., copper) is placed at the anode.

3. **Oxidation at the Anode**:
- At the anode, the impure metal oxidizes to form metal ions (e.g., Cu → Cu²⁺ + 2e⁻). The impurities present in the impure metal do not dissolve and instead settle at the bottom of the electrolytic cell, forming what is known as "anode mud".

4. **Reduction at the Cathode**:
- At the cathode, the metal ions (e.g., Cu²⁺) in the solution are reduced to form pure metal (e.g., Cu²⁺ + 2e⁻ → Cu). This pure metal is deposited on the cathode.

5. **Evaluating the Options**:
- **Option A**: "Impure metal is made of cathode" - Incorrect, as the cathode produces pure metal.
- **Option B**: "Impure metal is made of anode" - Correct, as the anode is where the impure metal is oxidized.
- **Option C**: "Impure metal is made of cathode and pure metal is made of anode" - Incorrect, as the cathode produces pure metal.
- **Option D**: "Both electrodes must be of pure metals" - Incorrect, as the anode is made of impure metal.

6. **Conclusion**:
- The correct answer is **Option B**: "Impure metal is made of anode".