Which can act as an oxidising as well as a reducing agent ?

Options

A. `HClO_(4)`
B. `HNO_(3)`
C. `H_(2)SO_(4)`
D. `H_(2)O_(2)`

Answer

To determine which substance can act as both an oxidizing agent and a reducing agent, we need to analyze the oxidation states of the elements in the given compounds. The key point is that a substance must not be in its highest or lowest oxidation state to exhibit both behaviors.

### Step-by-Step Solution:

1. **Understanding Oxidizing and Reducing Agents**:
- An oxidizing agent is a substance that gains electrons (is reduced) and typically has a high oxidation state.
- A reducing agent is a substance that loses electrons (is oxidized) and typically has a low oxidation state.

2. **Analyzing HClO4**:
- Calculate the oxidation state of Cl in HClO4:
- H: +1
- O: -2 (4 oxygen atoms contribute -8)
- Let the oxidation state of Cl be X.
- The equation becomes: +1 + X - 8 = 0 → X = +7.
- Since Cl is in its highest oxidation state (+7), HClO4 can only act as an oxidizing agent, not a reducing agent.

3. **Analyzing HNO3**:
- Calculate the oxidation state of N in HNO3:
- H: +1
- O: -2 (3 oxygen atoms contribute -6)
- Let the oxidation state of N be Y.
- The equation becomes: +1 + Y - 6 = 0 → Y = +5.
- Since N is in its highest oxidation state (+5), HNO3 can only act as an oxidizing agent, not a reducing agent.

4. **Analyzing H2SO4**:
- Calculate the oxidation state of S in H2SO4:
- H: +1 (2 hydrogen atoms contribute +2)
- O: -2 (4 oxygen atoms contribute -8)
- Let the oxidation state of S be Z.
- The equation becomes: +2 + Z - 8 = 0 → Z = +6.
- Since S is in its highest oxidation state (+6), H2SO4 can only act as an oxidizing agent, not a reducing agent.

5. **Analyzing H2O2**:
- Calculate the oxidation state of O in H2O2:
- H: +1 (2 hydrogen atoms contribute +2)
- Let the oxidation state of O be W.
- The equation becomes: +2 + 2W = 0 → 2W = -2 → W = -1.
- The oxidation state of O in H2O2 is -1, which is an intermediate state. Oxygen can exist in both -2 (in H2O) and 0 (in O2).
- Therefore, H2O2 can act as both an oxidizing agent (when it is reduced to H2O) and a reducing agent (when it is oxidized to O2).

6. **Conclusion**:
- The substance that can act as both an oxidizing agent and a reducing agent is **H2O2 (hydrogen peroxide)**.