The strongest acid is

Options

A. `HNO_2`
B. `HNO_3`
C. `H_2 N_2 O_2`
D. `HONS`

Explanation

To determine the strongest acid among the given options (HNO2, HNO3, H2N2O2, HONS), we will analyze the oxidation states of nitrogen in each compound. The strongest acid is typically the one with the highest oxidation state of the central atom (in this case, nitrogen).

### Step-by-Step Solution:

1. **Identify the Compounds**: The given options are:
- HNO2 (Nitrous acid)
- HNO3 (Nitric acid)
- H2N2O2 (Hydrazine)
- HONS (Thiohydroxylamine)

2. **Determine the Oxidation State of Nitrogen in Each Compound**:
- For **HNO2**:
- The oxidation state of nitrogen can be calculated as follows:
- Let the oxidation state of nitrogen be \( x \).
- The equation is: \( x + 2(-2) + 1 = 0 \) (where -2 is the oxidation state of oxygen)
- Solving gives: \( x - 4 + 1 = 0 \) → \( x = +3 \).

- For **HNO3**:
- Similarly, for HNO3:
- Let the oxidation state of nitrogen be \( x \).
- The equation is: \( x + 3(-2) + 1 = 0 \)
- Solving gives: \( x - 6 + 1 = 0 \) → \( x = +5 \).

- For **H2N2O2**:
- For H2N2O2:
- Let the oxidation state of nitrogen be \( x \).
- The equation is: \( 2x + 2(-2) = 0 \)
- Solving gives: \( 2x - 4 = 0 \) → \( x = +2 \) (for each nitrogen).

- For **HONS**:
- For HONS:
- Let the oxidation state of nitrogen be \( x \).
- The equation is: \( x + (-2) + 1 = 0 \)
- Solving gives: \( x - 1 = 0 \) → \( x = +1 \).

3. **Compare the Oxidation States**:
- HNO2: +3
- HNO3: +5
- H2N2O2: +1
- HONS: +1

4. **Conclusion**:
- The strongest acid is the one with the highest oxidation state of nitrogen, which is **HNO3** with an oxidation state of +5.

### Final Answer:
The strongest acid among the given options is **HNO3** (Nitric acid).