How many metals are commercially purified by Van Arkel method from the given metal ?
`Ti, B,Zr,Pb,Hg`.

Explanation

To solve the question of how many metals from the given list (Ti, B, Zr, Pb, Hg) are commercially purified by the Van Arkel method, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Van Arkel Method**: The Van Arkel method is a refining process used to obtain ultra-pure metals. It involves the formation of volatile metal iodides from the metal and iodine, which can then be decomposed to yield pure metal.

2. **Identify the Metals in the List**: The metals provided in the question are Titanium (Ti), Boron (B), Zirconium (Zr), Lead (Pb), and Mercury (Hg).

3. **Check Each Metal for Purification by Van Arkel Method**:
- **Titanium (Ti)**: This metal is known to be purified using the Van Arkel method. It forms titanium iodide (TiI4) which is volatile and can be decomposed to yield pure titanium.
- **Boron (B)**: Boron is not purified using the Van Arkel method. It does not form a volatile iodide suitable for this process.
- **Zirconium (Zr)**: Zirconium is also purified using the Van Arkel method. It forms zirconium iodide (ZrI4), which can be decomposed similarly to titanium.
- **Lead (Pb)**: Lead is not purified using the Van Arkel method. It does not form a suitable volatile iodide.
- **Mercury (Hg)**: Mercury is not purified using the Van Arkel method. It does not form a volatile iodide that can be decomposed in this manner.

4. **Count the Metals that Can Be Purified**: From the analysis, the metals that can be purified by the Van Arkel method are Titanium (Ti) and Zirconium (Zr).

5. **Conclusion**: Therefore, the total number of metals from the given list that are commercially purified by the Van Arkel method is 2.

### Final Answer:
**2** (The metals are Titanium and Zirconium).

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