Among the following the strongest acid is

Options

A. `H_3 PO_2`
B. `H_3 PO_3`
C. `H_3 PO_4`
D. `H_4 P_2 O_7`

Answer

To determine which of the given acids is the strongest, we will analyze the provided options based on their structures and acidic strengths.

### Step 1: Identify the Given Acids
The acids provided in the question are:
1. H₃PO₂ (Phosphorous acid)
2. H₃PO₃ (Phosphoric acid)
3. H₃PO₄ (Phosphoric acid)
4. H₄P₂O₇ (Pyrophosphoric acid)

### Step 2: Understand Acid Strength in Oxyacids
In oxyacids, the strength of the acid generally increases with the oxidation state of the central atom (in this case, phosphorus). Additionally, the presence of more P-OH bonds can lead to a decrease in acidity.

### Step 3: Analyze the Oxidation States
- **H₃PO₂**: Phosphorus has an oxidation state of +1.
- **H₃PO₃**: Phosphorus has an oxidation state of +3.
- **H₃PO₄**: Phosphorus has an oxidation state of +5.
- **H₄P₂O₇**: This compound can be viewed as a combination of two phosphoric acid units, with phosphorus in a +5 oxidation state.

### Step 4: Compare pKa Values
The strength of an acid can also be determined by its pKa value, where a lower pKa indicates a stronger acid:
- H₃PO₂: pKa ≈ 1.0
- H₃PO₃: pKa ≈ 1.4
- H₃PO₄: pKa ≈ 2.1
- H₄P₂O₇: The pKa can vary, but it is generally higher than that of H₃PO₄.

### Step 5: Conclusion
From the analysis:
- H₃PO₂ has the lowest pKa value (1.0), indicating it is the strongest acid among the options provided.
- Therefore, the strongest acid is **H₃PO₂**.

### Final Answer
The strongest acid among the given options is **H₃PO₂**.

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