Which pair contains both the phosphorius in +3 state ?

Options

A. Orthophosphorous and hypopospheric acids.
B. Pyrophosphorous and pyrophosphoric acids
C. Orthophosphorous and pyrophosphorous acids.
D. Pyrophosphorous and hypophosphoric acids.

Answer

To solve the question of which pair contains both phosphorus in the +3 oxidation state, we will analyze the oxidation states of phosphorus in the given acids step by step.

### Step 1: Identify the Compounds
The compounds mentioned in the question are:
1. Orthophosphorous acid
2. Hypophosphoric acid
3. Pyrophosphorous acid
4. Pyrophoric acid

### Step 2: Determine the Oxidation State of Phosphorus in Each Compound

#### Orthophosphorous Acid (H₃PO₃)
- The structure is H₃PO₃, where phosphorus is bonded to three hydrogen atoms and one oxygen atom (double bond).
- Assign oxidation states:
- Each H contributes +1 (3 H = +3).
- The double-bonded O contributes -2.
- Let the oxidation state of phosphorus be x.

The equation becomes:
\[ x + 3 - 2 = 0 \implies x + 1 = 0 \implies x = +3 \]

**Oxidation state of phosphorus in orthophosphorous acid = +3.**

#### Hypophosphoric Acid (H₄P₂O₆)
- The structure is H₄P₂O₆, where phosphorus is bonded to multiple oxygen atoms.
- Assign oxidation states:
- Each H contributes +1 (4 H = +4).
- The O contributes -2 (6 O = -12).
- Let the oxidation state of phosphorus be x.

The equation becomes:
\[ 2x + 4 - 12 = 0 \implies 2x - 8 = 0 \implies 2x = 8 \implies x = +4 \]

**Oxidation state of phosphorus in hypophosphoric acid = +4.**

#### Pyrophosphorous Acid (H₄P₂O₅)
- The structure is H₄P₂O₅, where phosphorus is bonded to oxygen atoms.
- Assign oxidation states:
- Each H contributes +1 (4 H = +4).
- The O contributes -2 (5 O = -10).
- Let the oxidation state of phosphorus be x.

The equation becomes:
\[ 2x + 4 - 10 = 0 \implies 2x - 6 = 0 \implies 2x = 6 \implies x = +3 \]

**Oxidation state of phosphorus in pyrophosphorous acid = +3.**

#### Pyrophoric Acid (H₄P₂O₇)
- The structure is H₄P₂O₇, where phosphorus is bonded to oxygen atoms.
- Assign oxidation states:
- Each H contributes +1 (4 H = +4).
- The O contributes -2 (7 O = -14).
- Let the oxidation state of phosphorus be x.

The equation becomes:
\[ 2x + 4 - 14 = 0 \implies 2x - 10 = 0 \implies 2x = 10 \implies x = +5 \]

**Oxidation state of phosphorus in pyrophoric acid = +5.**

### Step 3: Compare the Oxidation States
From our calculations:
- Orthophosphorous acid: +3
- Hypophosphoric acid: +4
- Pyrophosphorous acid: +3
- Pyrophoric acid: +5

### Conclusion
The pair that contains phosphorus in the +3 oxidation state is:
- Orthophosphorous acid (+3) and Pyrophosphorous acid (+3).

### Final Answer
The correct pair is **Orthophosphorous acid and Pyrophosphorous acid**.