Name the main method of purification employed for the purification of `Cu`, `Zn` and `Al`.

Explanation

To answer the question regarding the main method of purification employed for the purification of copper (Cu), zinc (Zn), and aluminum (Al), we can follow these steps:

### Step-by-Step Solution:

1. **Purification of Copper (Cu)**:
- The main method used for the purification of copper is **electrolytic refining**.
- In this process, impure copper is made the anode and a thin strip of pure copper is made the cathode.
- A solution of copper(II) sulfate is used as the electrolyte. When electric current passes through the solution, copper ions from the anode dissolve and deposit onto the cathode, resulting in purified copper.
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