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 each of the given acids based on their structure and the number of removable hydrogen ions they possess.

### Step-by-Step Solution:

1. **Identify the Acids**: The acids given in the options are:
- H3PO2 (Phosphorous acid)
- H3BO3 (Boric acid)
- H3PO4 (Phosphoric acid)
- H3PO3 (Phosphorous acid)

2. **Analyze H3PO2**:
- H3PO2 has only one removable hydrogen ion.
- When it reacts with a base (like NaOH), it forms only one type of salt: NaH2PO2.
- Therefore, H3PO2 does not form three series of salts.

3. **Analyze H3BO3**:
- H3BO3 is a Lewis acid and does not dissociate in the same way as traditional acids.
- It reacts with water to form BO(OH)4, and it can only form one type of salt.
- Thus, H3BO3 also does not form three series of salts.

4. **Analyze H3PO4**:
- H3PO4 is a tribasic acid, meaning it has three removable hydrogen ions.
- When it reacts with NaOH, it can form:
- First salt: NaH2PO4 (from one hydrogen ion)
- Second salt: Na2HPO4 (from two hydrogen ions)
- Third salt: Na3PO4 (from all three hydrogen ions)
- Therefore, H3PO4 can form three series of salts.

5. **Analyze H3PO3**:
- H3PO3 is a dibasic acid, meaning it has two removable hydrogen ions.
- When it reacts with NaOH, it can form:
- First salt: NaH2PO3 (from one hydrogen ion)
- Second salt: Na2HPO3 (from both hydrogen ions)
- Thus, H3PO3 can only form two series of salts.

6. **Conclusion**:
- The only acid that forms three series of salts is H3PO4 (Phosphoric acid).

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

---