Among the following ion the one that cannot undergo disproportionation

Options

A. `ClO^(-)`
B. `ClO_(2)^(-)`
C. `ClO_(3)^(-)`
D. `ClO_(4)^(-)`

Answer

To determine which ion cannot undergo disproportionation, we first need to understand what disproportionation is. A disproportionation reaction is a type of redox reaction in which a single substance is both oxidized and reduced, resulting in two different products with different oxidation states of the same element.

### Step-by-Step Solution:

1. **Identify the Oxidation States**:
We need to find the oxidation states of chlorine in each of the given ions. The ions we will analyze are:
- ClO⁻
- ClO₂⁻
- ClO₃⁻
- ClO₄⁻

2. **Calculate the Oxidation State for ClO⁻**:
- Let the oxidation state of Cl be \( x \).
- The equation becomes: \( x - 2 = -1 \) (since O has an oxidation state of -2).
- Solving for \( x \):
\[ x = -1 + 2 = +1 \]
- **Result**: The oxidation state of Cl in ClO⁻ is +1.

3. **Calculate the Oxidation State for ClO₂⁻**:
- Let the oxidation state of Cl be \( x \).
- The equation becomes: \( x - 2 \times 2 = -1 \).
- Solving for \( x \):
\[ x - 4 = -1 \implies x = +3 \]
- **Result**: The oxidation state of Cl in ClO₂⁻ is +3.

4. **Calculate the Oxidation State for ClO₃⁻**:
- Let the oxidation state of Cl be \( x \).
- The equation becomes: \( x - 3 \times 2 = -1 \).
- Solving for \( x \):
\[ x - 6 = -1 \implies x = +5 \]
- **Result**: The oxidation state of Cl in ClO₃⁻ is +5.

5. **Calculate the Oxidation State for ClO₄⁻**:
- Let the oxidation state of Cl be \( x \).
- The equation becomes: \( x - 4 \times 2 = -1 \).
- Solving for \( x \):
\[ x - 8 = -1 \implies x = +7 \]
- **Result**: The oxidation state of Cl in ClO₄⁻ is +7.

6. **Determine the Highest and Lowest Oxidation States**:
- The highest oxidation state of chlorine is +7 (in ClO₄⁻).
- The lowest oxidation state of chlorine is -1 (in Cl⁻).

7. **Check for Disproportionation**:
- For a species to undergo disproportionation, its oxidation state must be between the highest and lowest oxidation states.
- ClO⁻ (+1), ClO₂⁻ (+3), and ClO₃⁻ (+5) all have oxidation states between -1 and +7, so they can undergo disproportionation.
- ClO₄⁻ (+7) is at the highest oxidation state and cannot be oxidized further, thus it cannot undergo disproportionation.

### Conclusion:
The ion that cannot undergo disproportionation is **ClO₄⁻**.

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