Which of the following acids possesses oxidising, reducing, and complex forming properties ?

Options

A. `HNO_3`
B. `HNO_2`
C. `H_2 SO_4`
D. `HCl`

Answer

To determine which acid possesses oxidizing, reducing, and complex-forming properties, we need to analyze the oxidation states of the elements involved in the given acids. Let's go through the options step by step.

### Step 1: Understand Oxidizing and Reducing Agents
- An **oxidizing agent** is a substance that gets reduced (gains electrons) while causing another substance to be oxidized (lose electrons).
- A **reducing agent** is a substance that gets oxidized (loses electrons) while causing another substance to be reduced (gain electrons).

### Step 2: Analyze the Given Acids
We will analyze the oxidation states of nitrogen in the acids provided:

1. **HNO3 (Nitric Acid)**
- Oxidation state of nitrogen = +5
- Since +5 is the maximum oxidation state for nitrogen, it cannot be oxidized further. Therefore, it acts only as an oxidizing agent.

2. **HNO2 (Nitrous Acid)**
- Oxidation state of nitrogen = +3
- Nitrogen can be oxidized to +5 (acting as a reducing agent) and can also be reduced to -3 (acting as an oxidizing agent). Thus, HNO2 can act as both an oxidizing and reducing agent.

3. **H2SO4 (Sulfuric Acid)**
- Oxidation state of sulfur = +6
- Similar to HNO3, since +6 is the maximum oxidation state for sulfur, it cannot be oxidized further. Therefore, it acts only as an oxidizing agent.

4. **HCl (Hydrochloric Acid)**
- Oxidation state of chlorine = -1
- This is the minimum oxidation state for chlorine, so it cannot act as an oxidizing agent. It does not possess reducing properties either.

### Step 3: Conclusion
From the analysis:
- **HNO3**: Oxidizing agent only.
- **HNO2**: Acts as both an oxidizing and reducing agent.
- **H2SO4**: Oxidizing agent only.
- **HCl**: Neither oxidizing nor reducing agent.

Thus, the acid that possesses oxidizing, reducing, and complex-forming properties is **HNO2 (Nitrous Acid)**.

### Final Answer
**HNO2 (Nitrous Acid)** possesses oxidizing, reducing, and complex-forming properties.

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