Which conversion is an oxidation?

Options

A. `SO_4^2⁻ to SO_3^(2-)`
B. `Cu^(2^+) to Cu`
C. `H^+ to H`
D. `H^- to H`

Explanation

To determine which conversion represents oxidation, we need to analyze the changes in oxidation states for each of the given reactions. Oxidation is defined as an increase in oxidation state.

### Step-by-Step Solution:

1. **Identify the reactions and their oxidation states**:
- **Reaction A**: \( \text{SO}_4^{2-} \rightarrow \text{SO}_3^{2-} \)
- **Reaction B**: \( \text{Cu}^{2+} \rightarrow \text{Cu} \)
- **Reaction C**: \( \text{H}^+ \rightarrow \text{H} \)
- **Reaction D**: \( \text{H}^- \rightarrow \text{H} \)

2. **Calculate the oxidation states for each reaction**:
- **Reaction A**:
- For \( \text{SO}_4^{2-} \): Let the oxidation state of sulfur be \( x \).
\[ x + 4(-2) = -2 \implies x - 8 = -2 \implies x = +6 \]
- For \( \text{SO}_3^{2-} \): Let the oxidation state of sulfur be \( y \).
\[ y + 3(-2) = -2 \implies y - 6 = -2 \implies y = +4 \]
- Change in oxidation state: \( +6 \) to \( +4 \) (decrease, reduction).

- **Reaction B**:
- For \( \text{Cu}^{2+} \): Oxidation state is \( +2 \).
- For \( \text{Cu} \): Oxidation state is \( 0 \).
- Change in oxidation state: \( +2 \) to \( 0 \) (decrease, reduction).

- **Reaction C**:
- For \( \text{H}^+ \): Oxidation state is \( +1 \).
- For \( \text{H} \): Oxidation state is \( 0 \).
- Change in oxidation state: \( +1 \) to \( 0 \) (decrease, reduction).

- **Reaction D**:
- For \( \text{H}^- \): Oxidation state is \( -1 \).
- For \( \text{H} \): Oxidation state is \( 0 \).
- Change in oxidation state: \( -1 \) to \( 0 \) (increase, oxidation).

3. **Determine which reaction is oxidation**:
- From the analysis, only **Reaction D** shows an increase in oxidation state from \( -1 \) to \( 0 \), which indicates oxidation.

### Final Answer:
The conversion that is an oxidation is **Reaction D: \( \text{H}^- \rightarrow \text{H} \)**.

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