How many metals are commercially extracted by electrometallury form the given metals ?
`Al, Mg, Na, K, Ag`.

Explanation

To determine how many metals from the given list (Al, Mg, Na, K, Ag) are commercially extracted by electrometallurgy, we will analyze each metal based on its extraction method.

### Step-by-Step Solution:

1. **Understanding Electrometallurgy**: Electrometallurgy involves the extraction of metals using electrolysis, particularly for highly electropositive metals that cannot be reduced by conventional methods.

2. **Analyzing Each Metal**:
- **Aluminum (Al)**:
- Aluminum is extracted from its oxide (Al₂O₃) using electrolysis. The process requires high temperatures and is not feasible with a normal reducing agent. Therefore, aluminum is extracted by electrometallurgy.

- **Magnesium (Mg)**:
- Magnesium is obtained from magnesium chloride (MgCl₂) through electrolysis. Similar to aluminum, it is highly electropositive and cannot be extracted using a conventional reducing agent. Thus, magnesium is also extracted by electrometallurgy.

- **Sodium (Na)**:
- Sodium is extracted from rock salt (NaCl) using electrolysis. It is highly reactive and cannot be obtained by normal reduction methods, confirming that sodium is extracted by electrometallurgy.

- **Potassium (K)**:
- Potassium is also extracted through electrolysis from potassium chloride (KCl). Like sodium, it is highly electropositive and requires electrolysis for extraction. Therefore, potassium is included in the list of metals extracted by electrometallurgy.

- **Silver (Ag)**:
- Silver is primarily extracted using the cyanide process from silver sulfide (Ag₂S). This method does not involve electrolysis and is suitable for less reactive metals. Hence, silver is not extracted by electrometallurgy.

3. **Counting the Metals**:
- From the analysis, the metals that are extracted by electrometallurgy are Aluminum (Al), Magnesium (Mg), Sodium (Na), and Potassium (K). This gives us a total of 4 metals.

### Final Answer:
**4 metals are commercially extracted by electrometallurgy from the given metals: Al, Mg, Na, and K.**

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