The oxidation of manganate ion to permanganate ion can be done by

Options

A. `Cl_(2)`
B. `H_(2)`
C. `SO_(2)`
D. `KNO_(3)`

Answer

To determine how the oxidation of the manganate ion (MnO4^2-) to permanganate ion (MnO4^-) can be achieved, we will analyze the options provided: Cl2, H2, SO2, and KNO3.

### Step-by-Step Solution:

1. **Identify the oxidation states**:
- The oxidation state of manganese in the manganate ion (MnO4^2-) can be calculated as follows:
\[ x + 4(-2) = -2 \quad \text{(where x is the oxidation state of Mn)} \]
\[ x - 8 = -2 \implies x = +6 \]
- For the permanganate ion (MnO4^-):
\[ y + 4(-2) = -1 \quad \text{(where y is the oxidation state of Mn)} \]
\[ y - 8 = -1 \implies y = +7 \]
- Thus, Mn is oxidized from +6 in MnO4^2- to +7 in MnO4^-.

2. **Evaluate the oxidation agents**:
- **Option A: Cl2**:
- Chlorine gas (Cl2) is a strong oxidizing agent and can oxidize MnO4^2- to MnO4^-.
- The balanced reaction is:
\[ K2MnO4 + Cl2 \rightarrow 2KMnO4 + 2KCl \]
- This reaction confirms that Cl2 can oxidize the manganate ion to permanganate ion.

- **Option B: H2**:
- Hydrogen gas (H2) does not act as an oxidizing agent for MnO4^2- and does not participate in this reaction.
- Therefore, H2 cannot oxidize MnO4^2- to MnO4^-.

- **Option C: SO2**:
- Sulfur dioxide (SO2) reacts with MnO4^2- to form manganese(II) sulfate (MnSO4), not permanganate.
- The reaction is:
\[ K2MnO4 + SO2 \rightarrow MnSO4 + K2SO4 \]
- Thus, SO2 does not oxidize MnO4^2- to MnO4^-.

- **Option D: KNO3**:
- Potassium nitrate (KNO3) does not oxidize the manganate ion. Instead, K2MnO4 reacts with KNO2 in the presence of water to produce manganese dioxide (MnO2) and KNO3.
- The reaction is:
\[ K2MnO4 + KNO2 + H2O \rightarrow MnO2 + KNO3 + 2KOH \]
- Therefore, KNO3 does not facilitate the oxidation to permanganate.

3. **Conclusion**:
- The only viable option that can oxidize the manganate ion (MnO4^2-) to permanganate ion (MnO4^-) is **Cl2**.

### Final Answer:
The oxidation of manganate ion to permanganate ion can be done by **Cl2**.