Which of the following is a tetrabasic acid?

Options

A. Hypophosphorous acid
B. Metaphosphoric acid
C. Pyrophosphoric acid
D. Orthophosphoric acid

Answer

To determine which of the given options is a tetrabasic acid, we need to identify the number of hydrogen ions (H⁺) that each acid can donate. A tetrabasic acid is defined as one that can donate four H⁺ ions.

### Step-by-Step Solution:

1. **Understand the Definition of Tetrabasic Acid**:
- A tetrabasic acid can donate four H⁺ ions. Therefore, we need to analyze each option to count the number of H⁺ ions they can release.

2. **Evaluate the First Option: Hypo-phosphorylase Acid (H₃O₂)**:
- The formula is H₃O₂.
- Count the number of OH⁻ ions: There is only one OH⁻ ion.
- Conclusion: This is a **monobasic acid** (can donate 1 H⁺).

3. **Evaluate the Second Option: Phosphoric Acid (H₃PO₃)**:
- The formula is H₃PO₃.
- Structure: P double bond O, OH, and OH.
- Count the number of OH⁻ ions: There is only one OH⁻ ion.
- Conclusion: This is also a **monobasic acid** (can donate 1 H⁺).

4. **Evaluate the Third Option: Pyrophosphoric Acid (H₄P₂O₇)**:
- The formula is H₄P₂O₇.
- Structure: P double bond O, O, P, O, and OH groups.
- Count the number of OH⁻ ions: There are four OH⁻ ions.
- Conclusion: This is a **tetrabasic acid** (can donate 4 H⁺).

5. **Evaluate the Fourth Option: Orthophosphoric Acid (H₃PO₄)**:
- The formula is H₃PO₄.
- Structure: P double bond O, OH, OH, and OH.
- Count the number of OH⁻ ions: There are three OH⁻ ions.
- Conclusion: This is a **tri-basic acid** (can donate 3 H⁺).

6. **Final Conclusion**:
- Among the options evaluated, **Pyrophosphoric Acid (H₄P₂O₇)** is the only tetrabasic acid as it can donate four H⁺ ions.

### Answer:
The tetrabasic acid from the options provided is **Pyrophosphoric Acid (H₄P₂O₇)**.