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 its ability to form volatile compounds and decompose back to pure metal.

### Step-by-Step Solution:

1. **Understanding Vapor Phase Refining**:
- Vapor phase refining is a method used to purify metals by converting them into volatile compounds, which can then be decomposed to yield pure metal.
- The metal must be able to form a volatile compound with a suitable reagent and must also decompose easily to revert to its pure metallic form.

2. **Analyzing Each Metal**:
- **Nickel (Ni)**: Nickel can be purified by vapor phase refining as it forms volatile nickel carbonyl (Ni(CO)4) when reacted with carbon monoxide. This compound can be decomposed to yield pure nickel.
- **Titanium (Ti)**: Titanium can also be purified using vapor phase refining. It forms volatile titanium tetrachloride (TiCl4) when reacted with chlorine, which can be decomposed to obtain pure titanium.
- **Zirconium (Zr)**: Zirconium can be purified by vapor phase refining as well. It forms zirconium tetrachloride (ZrCl4), which is volatile and can be decomposed to yield pure zirconium.
- **Germanium (Ge)**: Germanium does not typically undergo vapor phase refining as it does not form a suitable volatile compound that can be easily decomposed.
- **Indium (In)**: Indium does not form a volatile compound suitable for vapor phase refining.
- **Iron (Fe)**: Iron does not form a volatile compound that can be used in vapor phase refining.
- **Copper (Cu)**: Copper does not form a volatile compound that can be purified by this method.
- **Gold (Au)**: Gold does not form a volatile compound suitable for vapor phase refining.

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

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