Which of the following acids forms three series of salts ?

Options

A. `H_(3)PO_(2)`
B. `H_(3)BO_(3)`
C. `H_(3)PO_(4)`
D. `H_(3)PO_(3)`

Explanation

To determine which acid forms three series of salts, we need to analyze the basicity of the acids provided in the options. The basicity of an acid refers to the number of hydrogen ions (H⁺) it can donate.

### Step-by-Step Solution:

1. **Understanding Basicity**:
- Basicity is defined as the number of H⁺ ions an acid can donate. An acid that can donate three H⁺ ions can form three series of salts.

2. **Analyzing the Acids**:
- Let's consider the acids mentioned in the question:
- H₃PO₂ (Phosphorous acid)
- H₃PO₃ (Phosphoric acid)
- H₃PO₄ (Phosphoric acid)
- H₃BO₃ (Boric acid)

3. **Examining H₃PO₂**:
- The structure of H₃PO₂ shows that it can donate only 1 H⁺ ion due to the presence of one hydroxyl group (OH) and two other hydrogen atoms that do not dissociate. Therefore, it can form only one series of salts.

4. **Examining H₃PO₃**:
- The structure of H₃PO₃ indicates that it can donate 2 H⁺ ions. Hence, it can form two series of salts.

5. **Examining H₃PO₄**:
- H₃PO₄ has three hydroxyl groups (OH) and can donate 3 H⁺ ions. This means it can form three series of salts:
- H₃PO₄ → H₂PO₄⁻ → HPO₄²⁻ → PO₄³⁻
- Therefore, H₃PO₄ is capable of forming three series of salts.

6. **Examining H₃BO₃**:
- H₃BO₃ (Boric acid) can donate only 1 H⁺ ion and thus can form only one series of salts.

7. **Conclusion**:
- Based on the analysis, the only acid that can form three series of salts is H₃PO₄ (Phosphoric acid).

### Final Answer:
The acid that forms three series of salts is **H₃PO₄**.