Which of the following acts as an oxidising as well as reducing agent ?

Options

A. `Na_(2)O`
B. `H_2SO_4`
C. `HNO_3`
D. `HNO_2`

Answer

To determine which of the following acts as both an oxidizing agent and a reducing agent, we need to analyze the oxidation states of the elements involved. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Definitions
- **Oxidizing Agent**: A substance that can gain electrons (be reduced) and, in the process, oxidizes another substance.
- **Reducing Agent**: A substance that can lose electrons (be oxidized) and, in the process, reduces another substance.

### Step 2: Identify the Elements
We will consider common elements and compounds that are known to have variable oxidation states, particularly from the p-block of the periodic table.

### Step 3: Analyze Oxidation States
1. **Nitrogen (N)**:
- Nitrogen has 5 valence electrons.
- Its oxidation state can vary from -3 (in NH3) to +5 (in HNO3).
- Therefore, nitrogen can act as a reducing agent when it goes from +3 to +5 (losing electrons) and as an oxidizing agent when it goes from +3 to -3 (gaining electrons).

2. **Sulfur (S)**:
- Sulfur has 6 valence electrons.
- Its oxidation state can vary from -2 (in H2S) to +6 (in H2SO4).
- However, sulfur cannot act as both an oxidizing and reducing agent in the same way as nitrogen because it cannot easily transition from +6 to a lower oxidation state while also being able to oxidize other substances.

3. **HNO3 (Nitric Acid)**:
- In HNO3, nitrogen is in the +5 oxidation state.
- It cannot be reduced further to act as a reducing agent, hence it cannot serve both roles.

### Step 4: Conclusion
From the analysis above, **Nitrogen** is the element that can act as both an oxidizing agent and a reducing agent due to its ability to exist in multiple oxidation states.

### Final Answer:
**Nitrogen (N)** acts as both an oxidizing agent and a reducing agent.

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