Which is dibasic?

Options

A. Orthosphoric acid
B. Pyrophosphoric acid
C. phosphorus acid
D. Hypophosphorus acid

Answer

To determine which acid is dibasic among the given options, we need to analyze the structure and the number of replaceable hydrogen ions (H⁺) in each acid. A dibasic acid is defined as an acid that can donate two protons (H⁺ ions).

### Step-by-Step Solution:

1. **Identify the Acids and Their Formulas**:
- Orthophosphoric acid: H₃PO₄
- Pyrophosphoric acid: H₄P₂O₇
- Phosphorous acid: H₃PO₃
- Hypophosphorous acid: H₃PO₂

2. **Analyze Orthophosphoric Acid (H₃PO₄)**:
- Structure: P(=O)(OH)₃
- It has three acidic hydrogen atoms (H⁺), so it is **trihydric** (not dibasic).

3. **Analyze Pyrophosphoric Acid (H₄P₂O₇)**:
- Structure: P(=O)(OH)₂-O-P(=O)(OH)₂
- It has four acidic hydrogen atoms (H⁺), thus it is **tetrahydric** (not dibasic).

4. **Analyze Phosphorous Acid (H₃PO₃)**:
- Structure: P(=O)(OH)₂-H
- It has two acidic hydrogen atoms (H⁺) attached to oxygen, making it **dibasic**.

5. **Analyze Hypophosphorous Acid (H₃PO₂)**:
- Structure: P(=O)(OH)-H(OH)
- It has only one acidic hydrogen atom (H⁺), so it is **monobasic** (not dibasic).

6. **Conclusion**:
- Among the given acids, **Phosphorous acid (H₃PO₃)** is the only dibasic acid as it has two replaceable hydrogen ions.

### Final Answer:
**Phosphorous acid (H₃PO₃) is dibasic.**