How many metals are commercially purified by electrolysis method from the given metals ?
`Na, Al, Pb, Ni`.

Explanation

To determine how many metals from the given list (Na, Al, Pb, Ni) are commercially purified by the electrolysis method, we can analyze each metal based on its properties and the purification process.

### Step-by-Step Solution:

1. **Understanding Electrolysis**:
- Electrolysis is a method used to purify metals, especially those that are highly electropositive and cannot be easily reduced by conventional methods.

2. **Analyzing Sodium (Na)**:
- Sodium is a highly reactive metal and is typically found in nature as sodium chloride (NaCl).
- It is purified by electrolysis because it is highly electropositive and cannot be reduced easily through other methods.
- **Conclusion**: Sodium is purified by electrolysis.

3. **Analyzing Aluminum (Al)**:
- Aluminum is found as aluminum oxide (Al2O3) in nature.
- Due to its high electropositivity, aluminum cannot be reduced easily, and electrolysis is used for its purification.
- **Conclusion**: Aluminum is purified by electrolysis.

4. **Analyzing Lead (Pb)**:
- Lead is commonly found as lead sulfide (galena).
- It can be reduced easily using methods such as roasting and reduction with carbon, rather than electrolysis.
- **Conclusion**: Lead is not purified by electrolysis.

5. **Analyzing Nickel (Ni)**:
- Nickel can be found as nickel chloride, and it can be reduced using more electropositive metals like zinc.
- Although electrolysis can be applied, it is not the primary method for commercial purification of nickel.
- **Conclusion**: Nickel is not primarily purified by electrolysis.

6. **Final Count**:
- From the analysis, the metals that are commercially purified by electrolysis are Sodium and Aluminum.
- Therefore, the total number of metals purified by electrolysis from the given list is **2**.

### Final Answer:
The number of metals that are commercially purified by electrolysis from the given metals (Na, Al, Pb, Ni) is **2**.

---