Vapour phase refining can be carried out in case of

Options

A. Ni
B. Zr
C. Ti
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Vapor Phase Refining**:
- Vapor phase refining is a method used to purify certain metals. It involves converting the crude metal into a volatile compound, which is then decomposed to yield the pure metal.

2. **Process of Vapor Phase Refining**:
- The process consists of two main steps:
- **Conversion to Volatile Compound**: The impure metal is transformed into a volatile compound.
- **Thermal Decomposition**: The volatile compound is then subjected to high temperatures to decompose it back into the pure metal.

3. **Examples of Metals**:
- We will analyze the metals provided in the options:
- **Nickel**: Nickel can be refined using the Mond process, where it is converted into nickel tetracarbonyl (Ni(CO)₄), which is volatile. Upon thermal decomposition, it yields pure nickel and carbon monoxide (CO).
- **Zirconium**: Zirconium can be refined using the Van Arkel process, where it is converted into zirconium tetraiodide (ZrI₄). This compound is also volatile and decomposes to give pure zirconium and iodine (I₂).
- **Titanium**: Similar to zirconium, titanium can be refined using the Van Arkel process by converting it into titanium tetraiodide (TiI₄), which decomposes to yield pure titanium and iodine (I₂).

4. **Conclusion**:
- Since all three metals (nickel, zirconium, and titanium) can undergo vapor phase refining, the correct answer to the question is that vapor phase refining can be carried out for all of these metals.

5. **Final Answer**:
- The correct option is **4. All of these**.