Which of the following is an allotrope of oxygen ?

Options

A. O
B. `O_4`
C. `O_3`
D. `O^(2-)`

Explanation

To determine which of the following is an allotrope of oxygen, we need to understand the concept of allotropes and identify the forms of oxygen that exist.

### Step-by-Step Solution:

1. **Understanding Allotropes**: Allotropes are different forms of the same element that exist in the same physical state. For example, carbon can exist as diamond, graphite, and fullerenes. Each of these forms has distinct physical and chemical properties.

2. **Identifying Forms of Oxygen**: Oxygen can exist in several forms. The most common forms are:
- O2 (dioxygen)
- O3 (ozone)
- O (atomic oxygen)
- Various oxides such as CO (carbon monoxide), NO (nitric oxide), etc.

3. **Analyzing the Options**:
- If the options provided include O2, O3, and possibly other compounds or forms, we need to identify which of these is an allotrope.
- O2 is the most common form of oxygen but is not an allotrope; it is the diatomic molecule of oxygen.
- O3, known as ozone, is a recognized allotrope of oxygen.

4. **Conclusion**: Based on the definitions and the forms of oxygen, the correct allotrope of oxygen from the options is O3 (ozone).

### Final Answer:
The allotrope of oxygen is **O3 (ozone)**.