The maximum number of reducing hydrogens are contained in which of the following molecule/s ?

Options

A. `H_3PO_3`
B. `H_3PO_2`
C. `H_4P_2O_7`
D. `H_4PO_4`

Answer

To determine the maximum number of reducing hydrogens in the given molecules, we will analyze each molecule and count the number of hydrogen atoms that are directly attached to the phosphorus (P) atom.

### Step-by-Step Solution:

1. **Understanding Reducing Hydrogens**:
Reducing hydrogens are those hydrogen atoms that are directly bonded to the central atom (in this case, phosphorus).

2. **Analyzing H3PO3 (Phosphorous Acid)**:
- Structure: H3PO3 has the formula where phosphorus is bonded to three hydrogen atoms and one oxygen atom.
- Directly attached H to P: Only one hydrogen is directly attached to phosphorus.
- **Count**: 1 reducing hydrogen.

3. **Analyzing H3PO2 (Hypophosphorous Acid)**:
- Structure: H3PO2 has the formula where phosphorus is bonded to two hydrogen atoms and one oxygen atom.
- Directly attached H to P: Two hydrogens are directly attached to phosphorus.
- **Count**: 2 reducing hydrogens.

4. **Analyzing H3PO4 (Phosphoric Acid)**:
- Structure: H3PO4 has the formula where phosphorus is bonded to four oxygen atoms and no hydrogen atoms are directly attached to phosphorus.
- Directly attached H to P: Zero hydrogens are directly attached to phosphorus.
- **Count**: 0 reducing hydrogens.

5. **Analyzing H4P2O7 (Pyrophosphoric Acid)**:
- Structure: H4P2O7 has two phosphorus atoms and is bonded to several oxygen atoms.
- Directly attached H to P: Zero hydrogens are directly attached to phosphorus.
- **Count**: 0 reducing hydrogens.

6. **Conclusion**:
After analyzing all the molecules, the maximum number of reducing hydrogens is found in H3PO2, which has 2 reducing hydrogens.

### Final Answer:
The molecule with the maximum number of reducing hydrogens is **H3PO2**.

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