Zone refining is used to obtain metals in high degree of purity.
During electrorefining pure metal is liberated at the cathode.

Options

A. If both (A) and ( R) are correct and ( R) is the correct explanation of (A).
B. If both (A) and ( R) are correct, but ( R) is not the correct explanation of (A).
C. If (A) is correct, but ( R) is incorrect.
D. If (A) is incorrect, but ( R) is correct.

Answer

### Step-by-Step Solution:

1. **Understanding Zone Refining**:
- Zone refining is a method used to purify metals. It involves melting a small region (or zone) of an impure metal and moving this molten zone along the length of the metal rod. The impurities, which are more soluble in the molten state, move into the molten zone as it passes.

2. **Process of Zone Refining**:
- An impure metal rod is placed under a circular mobile heater. The heater melts a small section of the rod.
- As the heater moves along the rod, the molten zone also moves, carrying the impurities with it. The impurities are left behind in the solid metal as the molten zone progresses.

3. **Result of Zone Refining**:
- After several passes of the heater, the majority of impurities will have moved to one end of the rod, resulting in a highly purified metal at the other end.

4. **Understanding Electrorefining**:
- Electrorefining is another method used to purify metals, where an electric current is used to dissolve an impure metal (anode) and deposit pure metal (cathode).
- In the case of copper, for example, the anode is made of impure copper, and the cathode is made of pure copper.

5. **Process of Electrorefining**:
- During electrolysis, the impure copper at the anode dissolves into the solution as copper ions.
- These copper ions migrate through the solution and are reduced at the cathode, where they deposit as pure copper.

6. **Conclusion**:
- Both zone refining and electrorefining are effective methods for obtaining metals in high purity. The assertion that "zone refining is used to obtain metals in high degree of purity" is correct, and the reasoning that "during electrorefining pure metal is liberated at the cathode" is also correct. However, the reasoning does not directly explain the assertion.

### Final Answer:
Both the assertion and reasoning are correct, but the reasoning is not the correct explanation of the assertion.