Which change requires an oxidising agent?

Options

A. `2S_(2)O_(3)^(2-) iff S_(4)O_(6)^(2-)`
B. `Zn^(2+) iff Zn`
C. `ClO^(-) iff Cl^(-)`
D. `SO_(3) iff SO_(4)^(2-)`

Answer

To determine which change requires an oxidizing agent, we need to analyze the oxidation states of the elements involved in the given reactions. An oxidizing agent is a substance that causes oxidation by accepting electrons and, in the process, gets reduced itself. Here's a step-by-step solution:

### Step 1: Understand the Role of Oxidizing Agents
An oxidizing agent is required when there is an increase in the oxidation number of an element in a reaction. This means that one or more species in the reaction are losing electrons.

**Hint:** Remember that oxidation is the loss of electrons and is associated with an increase in oxidation state.

### Step 2: Analyze the Given Reactions
We need to look at each reaction and determine the oxidation states of the elements involved.

1. **Identify the oxidation states** of the elements in each reaction.
2. **Determine if there is an increase in oxidation state** for any of the elements.

**Hint:** Use the rules for assigning oxidation states, such as the oxidation state of oxygen is usually -2, and the sum of oxidation states in a neutral compound is zero.

### Step 3: Calculate Oxidation States
For each reaction, calculate the oxidation states of the relevant elements:

- For the first reaction involving sulfur, calculate the oxidation states of sulfur and oxygen.
- For the second reaction, analyze the change in oxidation state of chlorine and oxygen.
- Continue this for all reactions provided.

**Hint:** Write down the oxidation states for each element before and after the reaction to clearly see any changes.

### Step 4: Identify Changes in Oxidation States
After calculating the oxidation states, identify which elements have increased their oxidation numbers.

- If an element's oxidation state increases, it indicates that it has been oxidized and thus requires an oxidizing agent.

**Hint:** Look for elements that have gone from a lower oxidation state to a higher oxidation state.

### Step 5: Conclusion
Based on the analysis of the oxidation states, conclude which reaction requires an oxidizing agent.

- If you find an element that has increased its oxidation state, that reaction is the one that requires an oxidizing agent.

**Hint:** Summarize your findings by stating which reaction corresponds to an increase in oxidation state and thus requires an oxidizing agent.

### Final Answer
The change that requires an oxidizing agent is the one where the oxidation state of an element increases.