Metallic magnesium is prepared by-

Options

A. Reduction of `MgO` by coke
B. Electrolysis of aqueous solution of `Mg(NO_(3))_(2)`
C. Displacement of Mg by iron from `MgSO_(4)` solution
D. Electrolysis of molten `MgCI_(2)`

Answer

To determine how metallic magnesium is prepared, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compound**: The compound used for the preparation of metallic magnesium is magnesium chloride (MgCl₂).

2. **Electrolysis Process**: The preparation of metallic magnesium involves the process of electrolysis. This process requires the compound to be in a molten state.

3. **Electrolysis of Molten MgCl₂**: When molten MgCl₂ undergoes electrolysis, it dissociates into magnesium ions (Mg²⁺) and chloride ions (Cl⁻).

4. **Electrode Reactions**:
- **At the Cathode**: The magnesium ions (Mg²⁺) gain electrons (reduction) to form metallic magnesium (Mg).
\[ \text{Mg}^{2+} + 2e^- \rightarrow \text{Mg} \]
- **At the Anode**: The chloride ions (Cl⁻) lose electrons (oxidation) to form chlorine gas (Cl₂).
\[ 2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^- \]

5. **Overall Reaction**: The overall reaction during the electrolysis of molten MgCl₂ can be summarized as:
\[ \text{MgCl}_2 \rightarrow \text{Mg} + \text{Cl}_2 \]

6. **Conclusion**: Therefore, metallic magnesium is prepared by the electrolysis of molten magnesium chloride (MgCl₂).

### Final Answer:
Metallic magnesium is prepared by the electrolysis of molten MgCl₂.