Among the following acids , the one that can act as both an oxidizing agent and a reducing agent is

Options

A. `HNO_2`
B. `HClO_4`
C. `HNO_3`
D. `H_2SO_4`

Explanation

To solve the question of which acid can act as both an oxidizing agent and a reducing agent, we will analyze the oxidation states of the central atoms in the given acids.

### Step-by-Step Solution:

1. **Understanding Oxidizing and Reducing Agents**:
- An oxidizing agent is a substance that can accept electrons and get reduced, while a reducing agent is a substance that can donate electrons and get oxidized.

2. **Identify the Given Acids**:
- The acids we need to analyze are HNO2, HClO4, HNO3, and H2SO4.

3. **Calculate the Oxidation States**:
- **For HNO2**:
- Hydrogen (H) = +1
- Oxygen (O) = -2 (two oxygens contribute -4)
- Let the oxidation state of Nitrogen (N) be x.
- The equation becomes: +1 + x - 4 = 0 → x = +3.

- **For HClO4**:
- Hydrogen (H) = +1
- Oxygen (O) = -2 (four oxygens contribute -8)
- Let the oxidation state of Chlorine (Cl) be y.
- The equation becomes: +1 + y - 8 = 0 → y = +7.

- **For HNO3**:
- Hydrogen (H) = +1
- Oxygen (O) = -2 (three oxygens contribute -6)
- Let the oxidation state of Nitrogen (N) be z.
- The equation becomes: +1 + z - 6 = 0 → z = +5.

- **For H2SO4**:
- Hydrogen (H) = +1 (two hydrogens contribute +2)
- Oxygen (O) = -2 (four oxygens contribute -8)
- Let the oxidation state of Sulfur (S) be w.
- The equation becomes: +2 + w - 8 = 0 → w = +6.

4. **Analyzing the Oxidation States**:
- **HNO2**: N is in +3 oxidation state. It can either be oxidized to +5 or reduced to +2.
- **HClO4**: Cl is in +7 oxidation state. It can only be reduced.
- **HNO3**: N is in +5 oxidation state. It can only be reduced.
- **H2SO4**: S is in +6 oxidation state. It can only be reduced.

5. **Conclusion**:
- Among the acids, only HNO2 can act as both an oxidizing agent (by being oxidized from +3 to +5) and a reducing agent (by being reduced from +3 to +2). Therefore, the answer is **HNO2**.