During extraction of metals, electrolytic refining is used to obtain pure metals. During the process, the impure metal is made the anode and a thin strip of pure metal is made the cathode. The solution of the metal salt is used as an electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolves from the electrolyte. An equivalent of pure metal from the electrolyte is deposited on the cathode.
Which of the metals are refined by electrolytic refining?
I. Au
II. Cu
III. Na
IV. K

Options

A. I and II
B. I and III
C. II and III
D. II and IV

Explanation

To determine which metals can be refined by electrolytic refining, we need to analyze the properties of each metal listed in the question.

### Step 1: Understand the Process of Electrolytic Refining
Electrolytic refining involves using an impure metal as the anode and a pure metal strip as the cathode, with a metal salt solution as the electrolyte. When current is passed through the solution, the impure metal dissolves, and pure metal is deposited on the cathode.

### Step 2: Identify the Metals
The metals listed in the question are:
- I. Au (Gold)
- II. Cu (Copper)
- III. Na (Sodium)
- IV. K (Potassium)

### Step 3: Evaluate Each Metal
1. **Au (Gold)**: Gold can be refined using electrolytic refining due to its non-reactive nature and the ability to dissolve in specific electrolytes.
2. **Cu (Copper)**: Copper is commonly refined using electrolytic refining, as it is a good conductor and can easily be deposited from its salt solution.
3. **Na (Sodium)**: Sodium is highly reactive and is not refined through electrolytic refining. It is usually obtained through other methods, such as electrolysis of molten sodium chloride.
4. **K (Potassium)**: Similar to sodium, potassium is also highly reactive and cannot be refined using electrolytic refining.

### Step 4: Conclusion
Based on the evaluation, the metals that can be refined by electrolytic refining are:
- Au (Gold)
- Cu (Copper)

Thus, the answer is:
**I. Au and II. Cu**

### Final Answer
The metals refined by electrolytic refining are **I and II** (Au and Cu).

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