How many of these metals can be purified by vapour phase refining
`Ni, Ti, Zr, Ge, In, Fe, Cu, Au`

Answer

To determine how many of the given metals can be purified by vapor phase refining, we need to analyze each metal based on the two main processes of vapor phase refining: the Mons process and the Van Arkel method.

### Step-by-Step Solution:

1. **Understanding Vapor Phase Refining**:
- This method involves converting a metal into a volatile compound, which can then be decomposed to yield pure metal.
- The two key requirements are that the metal must form a volatile compound and that this compound should be easily decomposable.

2. **Analyzing Each Metal**:
- **Nickel (Ni)**:
- Nickel can be purified using the Mons process, where it is converted to nickel carbonyl (Ni(CO)4), which is volatile and can be decomposed to yield pure nickel.
- **Conclusion**: Nickel can be purified by vapor phase refining.

- **Titanium (Ti)**:
- Titanium can be purified using the Van Arkel method, where titanium iodide (TiI4) is formed, which is volatile and can be decomposed to yield pure titanium.
- **Conclusion**: Titanium can be purified by vapor phase refining.

- **Zirconium (Zr)**:
- Zirconium can also be purified using the Van Arkel method, similar to titanium, where zirconium iodide (ZrI4) is formed and decomposed to yield pure zirconium.
- **Conclusion**: Zirconium can be purified by vapor phase refining.

- **Germanium (Ge)**:
- Germanium does not form a volatile compound suitable for vapor phase refining.
- **Conclusion**: Germanium cannot be purified by vapor phase refining.

- **Indium (In)**:
- Indium can form volatile compounds, but it is not commonly purified by vapor phase refining.
- **Conclusion**: Indium cannot be purified by vapor phase refining.

- **Iron (Fe)**:
- Iron does not form a volatile compound that can be used for vapor phase refining.
- **Conclusion**: Iron cannot be purified by vapor phase refining.

- **Copper (Cu)**:
- Copper does not form a volatile compound suitable for vapor phase refining.
- **Conclusion**: Copper cannot be purified by vapor phase refining.

- **Gold (Au)**:
- Gold does not form a volatile compound that can be used for vapor phase refining.
- **Conclusion**: Gold cannot be purified by vapor phase refining.

3. **Final Count**:
- The metals that can be purified by vapor phase refining are: Nickel (Ni), Titanium (Ti), and Zirconium (Zr).
- Therefore, the total number of metals that can be purified by vapor phase refining from the given list is **3**.

### Summary:
**Answer**: 3 metals (Ni, Ti, Zr) can be purified by vapor phase refining.