Which change requires an oxidising agent?

Options

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

Explanation

To determine which change requires an oxidizing agent, we need to analyze the oxidation states of the elements involved in each option (A, B, C, D) and identify where oxidation occurs.

### Step-by-Step Solution:

1. **Understand the Role of an Oxidizing Agent**:
- An oxidizing agent facilitates oxidation by accepting electrons and, in the process, gets reduced itself. Therefore, we need to identify where oxidation is occurring in the given options.

2. **Analyze Option A**:
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