The oxyacid of phosphorous in which phosphorus has lowest oxidation state is.

Options

A. Hypophosphorus acid
B. Orthophosphoric acid
C. Pyrophosphoric acid
D. Metaphosphoric acid.

Explanation

To determine the oxyacid of phosphorus in which phosphorus has the lowest oxidation state, we can follow these steps:

### Step 1: Identify the Oxyacids of Phosphorus
The common oxyacids of phosphorus include:
1. Hypophosphorous acid (H₃PO₂)
2. Orthophosphoric acid (H₃PO₄)
3. Pyrophosphoric acid (H₄P₂O₇)
4. Metaphosphoric acid (HPO₃)

### Step 2: Determine the Oxidation States of Phosphorus in Each Acid
- **Hypophosphorous acid (H₃PO₂)**:
- The oxidation state of phosphorus can be calculated as follows:
- Let the oxidation state of phosphorus be x.
- The equation is: 3(+1) + x + 2(-2) = 0
- This simplifies to: 3 + x - 4 = 0 → x = +1.

- **Orthophosphoric acid (H₃PO₄)**:
- Using the same method:
- 3(+1) + x + 4(-2) = 0
- This simplifies to: 3 + x - 8 = 0 → x = +5.

- **Pyrophosphoric acid (H₄P₂O₇)**:
- For this acid:
- 4(+1) + 2x + 7(-2) = 0
- This simplifies to: 4 + 2x - 14 = 0 → 2x = 10 → x = +5.

- **Metaphosphoric acid (HPO₃)**:
- For this acid:
- (+1) + x + 3(-2) = 0
- This simplifies to: 1 + x - 6 = 0 → x = +5.

### Step 3: Compare the Oxidation States
From the calculations:
- Hypophosphorous acid has phosphorus in the +1 oxidation state.
- Orthophosphoric acid, pyrophosphoric acid, and metaphosphoric acid all have phosphorus in the +5 oxidation state.

### Conclusion
The oxyacid of phosphorus in which phosphorus has the lowest oxidation state is **Hypophosphorous acid (H₃PO₂)**, where phosphorus is in the +1 oxidation state.

### Final Answer
**Hypophosphorous acid (H₃PO₂)**

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