O.N. of P in pyrophosphoric acid is

Options

A. `+5`
B. `+2`
C. `+3`
D. `+4`

Answer

To find the oxidation number (O.N.) of phosphorus (P) in pyrophosphoric acid (H₄P₂O₇), we can follow these steps:

### Step-by-Step Solution:

1. **Write the formula of pyrophosphoric acid**:
The chemical formula is H₄P₂O₇.

2. **Identify the total charge of the molecule**:
Since pyrophosphoric acid is a neutral molecule, the total oxidation charge is zero.

3. **Assign oxidation numbers to known elements**:
- Hydrogen (H) typically has an oxidation number of +1.
- Oxygen (O) typically has an oxidation number of -2.

4. **Set up the equation**:
The total oxidation number can be expressed as:
\[ (O.N. \, of \, H) \times 4 + (O.N. \, of \, P) \times 2 + (O.N. \, of \, O) \times 7 = 0 \]
Substituting the known values:
\[ 4(+1) + 2(O.N. \, of \, P) + 7(-2) = 0 \]

5. **Simplify the equation**:
\[ 4 + 2(O.N. \, of \, P) - 14 = 0 \]
This simplifies to:
\[ 2(O.N. \, of \, P) - 10 = 0 \]

6. **Solve for the oxidation number of phosphorus**:
\[ 2(O.N. \, of \, P) = 10 \]
\[ O.N. \, of \, P = \frac{10}{2} = +5 \]

### Conclusion:
The oxidation number of phosphorus in pyrophosphoric acid (H₄P₂O₇) is +5.

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