Ultrapure Boron can be obtain when it is purified by

Options

A. Cupellation
B. Poling
C. Van Arkel
D. Zone refining

Answer

To determine how ultrapure boron can be obtained, we need to analyze the purification methods provided in the question.

### Step-by-Step Solution:

1. **Understanding the Purification Methods**:
- We have four methods to consider: Cupellation, Pauling method, Van Arkel method, and Zone refining.

2. **Evaluating Cupellation**:
- Cupellation is a process where impure metals are heated in a crucible, and impurities are oxidized and removed. This method is primarily used for lead purification in silver. Therefore, it is not suitable for obtaining ultrapure boron.

3. **Evaluating Pauling Method**:
- The Pauling method involves stirring molten impure metal with green wood poles containing hydrocarbons to remove oxides. This method is typically used for copper and tin purification. Hence, it is also not applicable for boron.

4. **Evaluating Van Arkel Method**:
- The Van Arkel method converts impure metals into volatile compounds, which are then decomposed electrically. This method is known for purifying metals like titanium and zirconium but is not specifically used for boron.

5. **Evaluating Zone Refining**:
- Zone refining is a technique used for the purification of metals like silicon, germanium, gallium, and boron. It relies on the differences in solubility of impurities in the molten and solid states. As the molten zone moves along the metal rod, pure metal crystallizes while impurities are left behind in the molten zone.

6. **Conclusion**:
- The method that can be used to obtain ultrapure boron is **Zone Refining**.

### Final Answer:
Ultrapure boron can be obtained when it is purified by **Zone Refining**.