`Cu^(2+)(aq.)` does not undergo redox reaction with solution:

Options

A. `(NH_(4))_(2)S`
B. `Na_(2)S_(2)O_(3)`
C. KI
D. `NH_(4)SCN`

Explanation

To determine which solution does not undergo a redox reaction with Cu²⁺, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Identify the options**: The options given are:
- Option 1: NH₄₂S
- Option 2: Na₂S₂O₃
- Option 3: KI
- Option 4: NH₄SCN

2. **Analyze Option 1: NH₄₂S**
- When Cu²⁺ reacts with NH₄₂S, it forms CuS.
- The oxidation state of Cu in both reactants and products remains +2.
- Since there is no change in oxidation state, this is **not a redox reaction**.

3. **Analyze Option 2: Na₂S₂O₃**
- When Cu²⁺ reacts with Na₂S₂O₃, it forms Cu₂S₂O₃.
- The oxidation state of Cu changes from +2 in the reactants to +1 in the products.
- This indicates a change in oxidation state, thus this is a **redox reaction**.

4. **Analyze Option 3: KI**
- When Cu²⁺ reacts with KI, it forms CuI and I₂.
- The oxidation state of Cu changes from +2 in the reactants to +1 in the products, and I changes from 0 to -1.
- This indicates a change in oxidation state, thus this is a **redox reaction**.

5. **Analyze Option 4: NH₄SCN**
- When Cu²⁺ reacts with NH₄SCN, it forms Cu(SCN)₂.
- The oxidation state of Cu changes from +2 in the reactants to +1 in the products.
- This indicates a change in oxidation state, thus this is a **redox reaction**.

6. **Conclusion**: Based on the analysis, the only option that does not undergo a redox reaction is **Option 1: NH₄₂S**.

### Final Answer:
**Cu²⁺ does not undergo a redox reaction with NH₄₂S.**

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