Complete the following by selecting the correct option from the choices given :
The divalent metal whose oxide is reduced to metal by electrolysis of its fused salt is ________ .(`Al//Na//Mg//K`)

Explanation

To solve the question, we need to identify the divalent metal from the options given and determine which of its oxides can be reduced to metal through the electrolysis of its fused salt.

### Step-by-Step Solution:

1. **Identify the Valency of Each Metal:**
- **Aluminium (Al)**: Aluminium has three valence electrons, making it trivalent (3+).
- **Sodium (Na)**: Sodium has one valence electron, making it monovalent (1+).
- **Magnesium (Mg)**: Magnesium has two valence electrons, making it divalent (2+).
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