How many of the following metals can be refined by vapour phase refining ?
`Zn,Zr,Hg,Cd,Ni,Ti,Co,Pt,Fe`.

Explanation

To determine how many of the given metals can be refined by vapor phase refining, we need to identify which of these metals can be converted into volatile compounds and subsequently purified through this method.

### Step-by-Step Solution:

1. **Understand Vapor Phase Refining**:
- Vapor phase refining involves converting a metal into a volatile compound, which can then be collected and decomposed to yield the pure metal.

2. **List the Metals**:
- The metals provided in the question are: Zn (Zinc), Zr (Zirconium), Hg (Mercury), Cd (Cadmium), Ni (Nickel), Ti (Titanium), Co (Cobalt), Pt (Platinum), Fe (Iron).

3. **Identify Metals Suitable for Vapor Phase Refining**:
- **Zinc (Zn)**: Typically refined by pyrometallurgical methods, not vapor phase refining.
- **Zirconium (Zr)**: Can be refined by vapor phase refining as it can form volatile compounds.
- **Mercury (Hg)**: Refined through distillation, not vapor phase refining.
- **Cadmium (Cd)**: Similar to zinc, it is not typically refined by vapor phase refining.
- **Nickel (Ni)**: Can be refined by vapor phase refining as it can form volatile nickel carbonyl.
- **Titanium (Ti)**: Can also be refined by vapor phase refining, specifically through the Kroll process.
- **Cobalt (Co)**: Not typically refined by vapor phase refining.
- **Platinum (Pt)**: Can be refined by vapor phase refining, but it is not commonly done.
- **Iron (Fe)**: Not refined by vapor phase refining.

4. **Count the Metals**:
- The metals that can be refined by vapor phase refining are: Zirconium (Zr), Nickel (Ni), and Titanium (Ti).
- Therefore, there are **three metals** that can be refined by vapor phase refining.

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

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