The acid which forms two series of salt is

Options

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

Answer

To determine the acid that forms two series of salts, we need to analyze the basicity of different acids. Basicity refers to the number of hydrogen ions (H⁺) that an acid can donate, which in turn indicates how many series of salts it can form.

### Step-by-Step Solution:

1. **Understanding Basicity**:
- Basicity is defined as the number of replaceable hydrogen ions (H⁺) in an acid. An acid with a basicity of 2 can donate two H⁺ ions, allowing it to form two series of salts.

2. **Identifying Candidate Acids**:
- We will consider several acids to determine their basicity:
- **H₃PO₄ (Phosphoric Acid)**:
- Basicity = 3 (can donate three H⁺ ions)
- Forms three series of salts.
- **H₃PO₃ (Phosphorous Acid)**:
- Basicity = 2 (can donate two H⁺ ions)
- Forms two series of salts.
- **H₃PO₂ (Hypophosphorous Acid)**:
- Basicity = 1 (can donate one H⁺ ion)
- Forms one series of salts.

3. **Analyzing the Results**:
- From the analysis, we see that:
- H₃PO₄ forms three series of salts.
- H₃PO₃ forms two series of salts.
- H₃PO₂ forms one series of salts.

4. **Conclusion**:
- The acid that forms two series of salts is **H₃PO₃ (Phosphorous Acid)**, as its basicity is 2.

### Final Answer:
The acid which forms two series of salts is **H₃PO₃ (Phosphorous Acid)**.

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