Which of the following is a neutral salt ?

Options

A. `NaH_(2)PO_(3)`
B. `NaH_(2)PO_(4)`
C. `NaH_(2)PO_(2)`
D. `Na_(2)H_(2)P_(2)O_(7)`

Answer

To determine which of the given compounds is a neutral salt, we need to analyze each option based on the presence of acidic hydrogen atoms. A neutral salt is formed when all acidic hydrogen atoms in an acid are replaced by metal cations, resulting in no remaining acidic hydrogen.

Let's analyze each option step by step:

### Step 1: Analyze Option 1 - NaH2PO3
- **Structure**: NaH2PO3 can be derived from phosphorous acid (H3PO3).
- **Acidic Hydrogens**: H3PO3 has two acidic hydrogens (the ones attached to oxygen).
- **Conclusion**: Since there is still one acidic hydrogen remaining after reacting with sodium, NaH2PO3 is not a neutral salt.

### Step 2: Analyze Option 2 - NaH3PO4
- **Structure**: NaH3PO4 can be derived from phosphoric acid (H3PO4).
- **Acidic Hydrogens**: H3PO4 has three acidic hydrogens.
- **Conclusion**: Since two acidic hydrogens remain after one reacts with sodium, NaH3PO4 is also not a neutral salt.

### Step 3: Analyze Option 3 - NaH2PO2
- **Structure**: NaH2PO2 can be derived from phosphinic acid (H3PO2).
- **Acidic Hydrogens**: H3PO2 has two acidic hydrogens.
- **Conclusion**: If one acidic hydrogen reacts with sodium, there will be no remaining acidic hydrogen. Thus, NaH2PO2 is a neutral salt.

### Step 4: Analyze Option 4 - Na2H4P2O7
- **Structure**: Na2H4P2O7 can be derived from diphosphoric acid (H4P2O7).
- **Acidic Hydrogens**: H4P2O7 has four acidic hydrogens.
- **Conclusion**: After reacting with sodium, there will still be two acidic hydrogens remaining. Therefore, Na2H4P2O7 is not a neutral salt.

### Final Conclusion
The only compound that qualifies as a neutral salt is **NaH2PO2**.

### Summary of the Solution
1. **NaH2PO3**: Contains one remaining acidic hydrogen - **Not neutral**.
2. **NaH3PO4**: Contains two remaining acidic hydrogens - **Not neutral**.
3. **NaH2PO2**: No remaining acidic hydrogens after reaction - **Neutral salt**.
4. **Na2H4P2O7**: Contains two remaining acidic hydrogens - **Not neutral**.

Thus, the correct answer is **NaH2PO2**.