Which of the following is a cyclic oxo acid ?

Options

A. `H_(4)P_(2)O_(7)`
B. `H_(4)P_(2)O_(6)`
C. `H_(3)P_(3)O_(9)`
D. `H_(5)P_(5)O_(15)`

Explanation

To determine which of the given options is a cyclic oxo acid, we need to analyze the definitions and characteristics of cyclic oxo acids and then evaluate the provided options.

### Step-by-Step Solution:

1. **Understanding Cyclic Oxo Acids**:
- Cyclic oxo acids are compounds that contain a ring structure and have one or more oxo (C=O) groups. They typically consist of a cyclic arrangement of atoms, including phosphorus and oxygen in this case.

2. **Identifying the Options**:
- The question refers to options that likely include different oxo acids of phosphorus. We need to focus on the specific structures of these acids to identify which one is cyclic.

3. **Analyzing the Given Compounds**:
- Let's consider the oxo acids of phosphorus mentioned in the video:
- HPO3 (Phosphorous acid)
- Cyclic compounds of phosphorus with varying numbers of phosphorus atoms (N=3 or N=5).

4. **Evaluating the Structures**:
- For N=3, the structure forms a 6-membered ring.
- For N=5, the structure forms a 10-membered ring.
- The cyclic structure for N=3 is more stable due to the smaller ring size.

5. **Drawing the Structure**:
- For the cyclic oxo acid with N=3:
- It consists of three phosphorus atoms arranged in a ring, with each phosphorus atom bonded to an oxygen atom and hydroxyl (OH) groups.

6. **Conclusion**:
- Based on the analysis, the cyclic oxo acid corresponds to the option with N=3, which forms a stable 6-membered ring structure.

### Final Answer:
The cyclic oxo acid is the one corresponding to N=3, which forms a 6-membered ring.