Which of the following is not a redox reaction ?

Options

A. `CuO+H_(2)rarrCu+H_(2)O`
B. `Na+H_(2)OrarrNaOH+1/2 H_(2)`
C. `CaCO_(3)rarr CaO+CO_(2)`
D. `2K+F_(2)rarr2KF`

Explanation

To determine which of the following reactions is not a redox reaction, we need to analyze each option and check for changes in oxidation states. A redox reaction involves both oxidation (loss of electrons) and reduction (gain of electrons).

### Step-by-Step Solution:

1. **Understanding Redox Reactions**:
- A redox reaction is characterized by the transfer of electrons between species, resulting in changes in their oxidation states. Oxidation refers to an increase in oxidation state, while reduction refers to a decrease in oxidation state.

2. **Analyzing the Reactions**:
- **Reaction 1**: Cu²⁺ + H₂ + O²⁻ → Cu + H⁺ + O²⁻
- Oxidation states: Cu goes from +2 to 0 (reduction), H goes from 0 to +1 (oxidation).
- Both oxidation and reduction occur, so this is a redox reaction.

- **Reaction 2**: NaOH + ½ H₂O → Na + H⁺ + O²⁻
- Oxidation states: Na goes from +1 to 0 (reduction), H goes from +1 to 0 (oxidation).
- Both oxidation and reduction occur, so this is a redox reaction.

- **Reaction 3**: CaCO₃ → CaO + CO₂
- Oxidation states: Ca remains +2, O remains -2, and C remains +4 throughout the reaction.
- No changes in oxidation states occur, so this is **not** a redox reaction.

- **Reaction 4**: K + F₂ → 2KF
- Oxidation states: K goes from 0 to +1 (oxidation), F goes from 0 to -1 (reduction).
- Both oxidation and reduction occur, so this is a redox reaction.

3. **Conclusion**:
- The reaction that does not involve a change in oxidation states is the third reaction: **CaCO₃ → CaO + CO₂**. Therefore, this is **not a redox reaction**.

### Final Answer:
The reaction that is not a redox reaction is **Reaction 3: CaCO₃ → CaO + CO₂**.

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