Consider the following metallurgical processes`:`
`(I)` Heating impure metal with `CO` and distilling the resulting volatile carbonyl `(b.p. 43^(@)C)` and finally decomposition at `150^(@)-200^(@)C` to get the pure metal.
`(II)` Heating the sulphide ore in air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged metal sulphide.
`(III)` Electrolysis of the molten electrolyte containing approximately equal amounts of the metal chloride and NaCl to obtain the metal.
The processes used for obtaining magnesium , nickel and copper are respectively.

Options

A. (I),(II) and (III)
B. (II), (III) and (I)
C. (III), (I) and (II)
D. (II), (I) and (III)

Explanation

To solve the question regarding the metallurgical processes used for obtaining magnesium, nickel, and copper, we will analyze each process step by step.

### Step 1: Analyzing Process I
- **Description**: Heating impure metal with carbon monoxide (CO) to form a volatile carbonyl, which is then distilled and decomposed at 150-200°C.
- **Application**: This process is specifically used for nickel. When nickel is heated with CO, it forms nickel carbonyl (Ni(CO)₄), which is a volatile compound. Upon distillation, the carbonyl is decomposed to yield pure nickel.

### Step 2: Analyzing Process II
- **Description**: Heating the sulphide ore in air until part of it is converted to oxide, followed by further heating in the absence of air to allow the oxide to react with unchanged metal sulphide.
- **Application**: This process is used for copper. The sulphide ore of copper (Cu₂S) is first roasted in the air, converting part of it to copper(I) oxide (Cu₂O) and releasing sulfur dioxide (SO₂). The remaining Cu₂S reacts with Cu₂O in the absence of air to produce pure copper and more SO₂.

### Step 3: Analyzing Process III
- **Description**: Electrolysis of a molten electrolyte containing approximately equal amounts of metal chloride and NaCl to obtain the metal.
- **Application**: This process is used for magnesium. The electrolysis of molten magnesium chloride (MgCl₂) mixed with NaCl allows for the separation of magnesium metal at the cathode.

### Conclusion
Based on the analysis of each process:
- Process I is used for obtaining **nickel**.
- Process II is used for obtaining **copper**.
- Process III is used for obtaining **magnesium**.

Thus, the order of processes for obtaining magnesium, nickel, and copper is **III - I - II**.

### Final Answer
The processes used for obtaining magnesium, nickel, and copper are respectively: **III (Magnesium), I (Nickel), II (Copper)**.

---