Which of the following is not correct ?

Options

A. `H_2O_2` oxidizes Fe (II) to Fe (III)
B. `H_2O_2` is a weak base
C. `H_2O_2` can be obtained by the electrolysis of dil . `H_2SO_4` .
D. `H_2O_2` reduces Mn (VII) to Mn (II)

Answer

To solve the question "Which of the following is not correct?" regarding the properties and reactions of \( S_2O_2 \) (disulfide peroxide) and \( H_2O_2 \) (hydrogen peroxide), we will analyze each option step by step.

### Step 1: Analyze the First Statement
**Statement:** \( S_2O_2 \) oxidizes \( Fe^{2+} \) to \( Fe^{3+} \).

**Reaction:**
\[ 2 Fe^{2+} + H_2O_2 + 4 OH^{-} \rightarrow 2 Fe(OH)_3 \]
- In this reaction, \( Fe^{2+} \) is oxidized to \( Fe^{3+} \).
- The oxidation state of \( Fe \) changes from +2 to +3, indicating that \( Fe^{2+} \) loses an electron.

**Conclusion:** This statement is correct.

### Step 2: Analyze the Second Statement
**Statement:** \( S_2O_2 \) is a weak base.

**pH Analysis:**
- The pH of \( H_2O_2 \) is given as 6.2.
- A pH less than 7 indicates that the solution is acidic, not basic.

**Conclusion:** This statement is incorrect. \( S_2O_2 \) is a weak acid, not a weak base.

### Step 3: Analyze the Third Statement
**Statement:** \( S_2O_2 \) can be obtained by the electrolysis of dilute \( H_2SO_4 \).

**Electrolysis Reaction:**
- The electrolysis of dilute \( H_2SO_4 \) produces \( H_2O_2 \) as a product.
- The reaction can be represented as:
\[ H_2SO_4 \rightarrow H_2O_2 + other products \]
- This indicates that \( S_2O_2 \) can indeed be formed through this process.

**Conclusion:** This statement is correct.

### Step 4: Analyze the Fourth Statement
**Statement:** \( H_2O_2 \) reduces \( Mn^{7+} \) to \( Mn^{2+} \).

**Reaction:**
\[ MnO_4^{-} + 3 e^{-} + 2 H_2O \rightarrow MnO_2 + 4 OH^{-} \]
- In this reaction, \( Mn \) is reduced from +7 to +2, indicating that \( H_2O_2 \) acts as a reducing agent.

**Conclusion:** This statement is correct.

### Final Conclusion
After analyzing all statements:
- The first statement is correct.
- The second statement is incorrect (as \( S_2O_2 \) is a weak acid).
- The third statement is correct.
- The fourth statement is correct.

Thus, the answer to the question "Which of the following is not correct?" is the **second statement**.