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. `(ii) & (iv)` shows oxidation

Answer

To solve the question, we need to analyze each of the given reactions to determine whether they involve oxidation or reduction.

### Step-by-Step Solution:

1. **Reaction (i): \( C_2O_4^{2-} \rightarrow CO_2 \)**
- Determine the oxidation state of carbon in \( C_2O_4^{2-} \):
- Let the oxidation state of carbon be \( x \).
- The equation becomes: \( 2x + 4(-2) = -2 \)
- Simplifying: \( 2x - 8 = -2 \) → \( 2x = 6 \) → \( x = +3 \) (for \( C_2O_4^{2-} \))
- Determine the oxidation state of carbon in \( CO_2 \):
- The equation becomes: \( x + 2(-2) = 0 \)
- Simplifying: \( x - 4 = 0 \) → \( x = +4 \) (for \( CO_2 \))
- Since the oxidation state of carbon increases from +3 to +4, this reaction involves **oxidation**.

2. **Reaction (ii): \( SO_4^{2-} \rightarrow SO_3^{2-} \)**
- Determine the oxidation state of sulfur in \( SO_4^{2-} \):
- Let the oxidation state of sulfur be \( x \).
- The equation becomes: \( x + 4(-2) = -2 \)
- Simplifying: \( x - 8 = -2 \) → \( x = +6 \) (for \( SO_4^{2-} \))
- Determine the oxidation state of sulfur in \( SO_3^{2-} \):
- The equation becomes: \( x + 3(-2) = -2 \)
- Simplifying: \( x - 6 = -2 \) → \( x = +4 \) (for \( SO_3^{2-} \))
- Since the oxidation state of sulfur decreases from +6 to +4, this reaction involves **reduction**.

3. **Reaction (iii): \( MnO_4^{2-} \rightarrow MnO_4^{-} \)**
- Determine the oxidation state of manganese in \( MnO_4^{2-} \):
- Let the oxidation state of manganese be \( x \).
- The equation becomes: \( x + 4(-2) = -2 \)
- Simplifying: \( x - 8 = -2 \) → \( x = +6 \) (for \( MnO_4^{2-} \))
- Determine the oxidation state of manganese in \( MnO_4^{-} \):
- The equation becomes: \( x + 4(-2) = -1 \)
- Simplifying: \( x - 8 = -1 \) → \( x = +7 \) (for \( MnO_4^{-} \))
- Since the oxidation state of manganese increases from +6 to +7, this reaction involves **oxidation**.

4. **Reaction (iv): \( Fe^{3+} \rightarrow Fe^{2+} \)**
- The oxidation state of iron decreases from +3 to +2.
- Since the oxidation state decreases, this reaction involves **reduction**.

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

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

### Final Answer:
**Option 3: Reactions (i) and (iii) show oxidation.**