Which of the following is not correct regarding the electrolyte preparation of `H_2O_2`?

Options

A. Lead used as cathode
B. `50% of H_2SO_4` is used
C. Hydrogen is liberated at anode
D. Sulphuric acid undergoes oxidation

Answer

To determine which statement is not correct regarding the electrolytic preparation of hydrogen peroxide (H₂O₂), we need to analyze the process involved in this preparation.

### Step-by-Step Solution:

1. **Understanding Electrolytic Preparation**:
The electrolytic preparation of H₂O₂ involves the electrolysis of sulfuric acid (H₂SO₄) solution. The key components are the electrolyte (H₂SO₄) and the electrodes (cathode and anode).

2. **Dissociation of Sulfuric Acid**:
When H₂SO₄ is dissolved in water, it dissociates into ions:
\[ H_2SO_4 \rightarrow 2H^+ + SO_4^{2-} \]

3. **Electrolysis Process**:
- At the **cathode** (negative electrode), hydrogen ions (H⁺) are reduced to form hydrogen gas (H₂):
\[ 2H^+ + 2e^- \rightarrow H_2 \]
- At the **anode** (positive electrode), the sulfate ions (SO₄²⁻) undergo oxidation, which can lead to the formation of peroxydisulfate (S₂O₈²⁻) or Marshall's acid (H₂S₂O₈):
\[ 2HSO_4^- \rightarrow H_2S_2O_8 + 2e^- \]

4. **Formation of Hydrogen Peroxide**:
The Marshall's acid (H₂S₂O₈) can hydrolyze to produce H₂O₂:
\[ H_2S_2O_8 + H_2O \rightarrow H_2SO_4 + H_2O_2 \]

5. **Identifying Incorrect Statements**:
Now, we analyze the options provided in the question to identify which statement is incorrect regarding the electrolytic preparation of H₂O₂.

- **Option 1**: "50% H₂SO₄ is used" - This is correct.
- **Option 2**: "Hydrogen is liberated at the cathode" - This is correct.
- **Option 3**: "Hydrogen is liberated at the anode" - This is incorrect, as hydrogen is liberated at the cathode, not the anode.
- **Option 4**: "Sulfuric acid undergoes oxidation" - This is correct.

6. **Conclusion**:
The incorrect statement regarding the electrolytic preparation of H₂O₂ is **Option 3**: "Hydrogen is liberated at the anode."