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

Options

A. `Na_2O`
B. `Na_2O_2`
C. `NaNO_3`
D. `NaNO_2`

Answer

To determine which of the given substances can act as both an oxidizing and reducing agent, we need to analyze the oxidation states of the elements in each compound.

### Step-by-Step Solution:

1. **Understanding Oxidizing and Reducing Agents**:
- An oxidizing agent is a substance that gains electrons and is reduced in the process.
- A reducing agent is a substance that loses electrons and is oxidized in the process.
- A substance that can act as both must be in an intermediate oxidation state, allowing it to either gain or lose electrons.

2. **Analyzing the Given Compounds**:
- **Na2O**: In sodium oxide (Na2O), oxygen has an oxidation state of -2. This is its minimum oxidation state, meaning it cannot act as a reducing agent (it cannot be oxidized further). Thus, it can only act as an oxidizing agent.

- **Na2O2**: In sodium peroxide (Na2O2), the oxidation state of oxygen is -1. This allows oxygen to either:
- Increase its oxidation state to 0 (acting as a reducing agent), or
- Decrease its oxidation state to -2 (acting as an oxidizing agent).
Hence, Na2O2 can act as both an oxidizing and reducing agent.

- **Na2O3**: In sodium oxide (Na2O3), nitrogen is in the +5 oxidation state. This is the maximum oxidation state for nitrogen, meaning it can only be reduced (not oxidized). Therefore, it cannot act as a reducing agent.

- **Na2O2 (with nitrogen)**: If we consider a nitrogen compound where nitrogen is in the +3 oxidation state, it can:
- Increase its oxidation state to +5 (acting as a reducing agent), or
- Decrease its oxidation state to -3 (acting as an oxidizing agent).
Thus, this compound can also act as both.

3. **Conclusion**:
- From the analysis, we find that Na2O2 can act as both an oxidizing and reducing agent. Additionally, the nitrogen compound with +3 oxidation state can also act as both. Therefore, the correct options are 2 and 4.

### Final Answer:
The substances that can act as both oxidizing and reducing agents are **Na2O2** and the nitrogen compound in the +3 oxidation state.