Consider the following reactions :
(i) `C_(2)O_(4)^(2-) rarr CO_(2)`
(ii) `SO_(4)^(2-) rarr SO_(3)^(2-)`
(iii) `MnO_(4)^(2-) rarr MnO_(4)^(-)`
(iv) `Fe^(3+) rarr Fe^(2+)`
Choose the correct answer -

Options

A. `(i) & (ii)` shows oxidation
B. `(iii) & (iv)` shows reduction
C. `(i) & (iii)` shows oxidation
D. `(iii) & (iv)` shows oxidation

Answer

To solve the problem, we need to analyze each of the given reactions to determine whether they represent oxidation or reduction processes.

### Step-by-Step Solution:

1. **Reaction (i): \( C_2O_4^{2-} \rightarrow CO_2 \)**
- **Determine Oxidation States:**
- For \( C_2O_4^{2-} \):
- Let the oxidation state of carbon be \( x \).
- The equation becomes: \( 2x + 4(-2) = -2 \)
- Solving gives \( 2x - 8 = -2 \) → \( 2x = 6 \) → \( x = +3 \).
- For \( CO_2 \):
- The oxidation state of carbon is \( +4 \).
- **Change in Oxidation State:**
- Carbon changes from \( +3 \) to \( +4 \) (loss of electrons).
- This indicates oxidation.

2. **Reaction (ii): \( SO_4^{2-} \rightarrow SO_3^{2-} \)**
- **Determine Oxidation States:**
- For \( SO_4^{2-} \):
- Let the oxidation state of sulfur be \( x \).
- The equation becomes: \( x + 4(-2) = -2 \)
- Solving gives \( x - 8 = -2 \) → \( x = +6 \).
- For \( SO_3^{2-} \):
- The equation becomes: \( x + 3(-2) = -2 \)
- Solving gives \( x - 6 = -2 \) → \( x = +4 \).
- **Change in Oxidation State:**
- Sulfur changes from \( +6 \) to \( +4 \) (gain of electrons).
- This indicates reduction.

3. **Reaction (iii): \( MnO_4^{2-} \rightarrow MnO_4^{-} \)**
- **Determine Oxidation States:**
- For \( MnO_4^{2-} \):
- Let the oxidation state of manganese be \( x \).
- The equation becomes: \( x + 4(-2) = -2 \)
- Solving gives \( x - 8 = -2 \) → \( x = +6 \).
- For \( MnO_4^{-} \):
- The equation becomes: \( x + 4(-2) = -1 \)
- Solving gives \( x - 8 = -1 \) → \( x = +7 \).
- **Change in Oxidation State:**
- Manganese changes from \( +6 \) to \( +7 \) (loss of electrons).
- This indicates oxidation.

4. **Reaction (iv): \( Fe^{3+} \rightarrow Fe^{2+} \)**
- **Change in Oxidation State:**
- Iron changes from \( +3 \) to \( +2 \) (gain of electrons).
- This indicates reduction.

### Summary of Changes:
- Reaction (i): Oxidation
- Reaction (ii): Reduction
- Reaction (iii): Oxidation
- Reaction (iv): Reduction

### Conclusion:
- The correct answer is that reactions (i) and (iii) show oxidation, while reactions (ii) and (iv) show reduction.