Which of the elements show allotropy ?

Options

A. B
B. P
C. As
D. Bi

Answer

To determine which elements among boron, phosphorus, arsenic, and bismuth show allotropy, we need to understand the concept of allotropy and analyze each element accordingly.

### Step-by-Step Solution:

1. **Understanding Allotropy**:
- Allotropy refers to the existence of an element in two or more different forms, known as allotropes, which have the same physical state but different physical properties.

2. **Analyzing Boron**:
- Boron exists in two allotropic forms: crystalline boron and amorphous boron. Therefore, boron shows allotropy.

3. **Analyzing Phosphorus**:
- Phosphorus has several allotropes, including white phosphorus, red phosphorus, and black phosphorus. Thus, phosphorus also exhibits allotropy.

4. **Analyzing Arsenic**:
- Arsenic has multiple allotropes as well, with six different forms identified. Therefore, arsenic shows allotropy.

5. **Analyzing Bismuth**:
- Bismuth does not exhibit allotropy. This is primarily due to the inert pair effect, which results in a lack of variable oxidation states that are necessary for allotropy to occur.

6. **Conclusion**:
- The elements that show allotropy among the given options are boron, phosphorus, and arsenic. Bismuth does not show allotropy.

### Final Answer:
- **Boron, Phosphorus, and Arsenic show allotropy. Bismuth does not.**