Which of the following does not represent redox reaction?

Options

A. `Cr_(2)O_(7)^(2-)+2overset(ɵ)(O)HtoCrO_(4)^(2-)+H_(2)O`
B. `SO_(5)^(2-)+2I^(ɵ)+2H^(o+)toI_(2)+SO_(4)^(2-)`
C. `2Ca(OH)_(2)+2Cl_(2)toCa(ClO)_(2)+CaCl_(2)+2H_(2)O`
D. `PCl_(5)toPCl_(3)+Cl_(2)`

Explanation

To determine which of the given reactions does not represent a redox reaction, we need to analyze each option based on the concept of oxidation and reduction. A redox reaction involves the transfer of electrons between species, leading to changes in their oxidation states.

### Step-by-Step Solution:

1. **Understand Redox Reactions**:
- Redox reactions involve oxidation (increase in oxidation state) and reduction (decrease in oxidation state) occurring simultaneously.
- Identify the oxidation states of the elements in the reactants and products.

2. **Analyze the First Reaction**:
- Reaction: Chromate reaction.
- Oxidation states:
- Chromate (Cr) is in +6 oxidation state on both sides.
- Oxygen is consistently in -2, and hydrogen is in +1.
- Conclusion: No change in oxidation states means this is not a redox reaction.

3. **Analyze the Second Reaction**:
- Reaction: Iodine and sulfur reaction.
- Oxidation states:
- Iodine changes from -1 to 0 (oxidation).
- Sulfur changes from +8 to +6 (reduction).
- Conclusion: Both oxidation and reduction occur, so this is a redox reaction.

4. **Analyze the Third Reaction**:
- Reaction: Calcium hydroxide and chlorine reaction.
- Oxidation states:
- Chlorine changes from 0 to -1 (reduction).
- Chlorine also has a +1 state in the product.
- Conclusion: Both oxidation and reduction occur, so this is a redox reaction.

5. **Analyze the Fourth Reaction**:
- Reaction: PCl5 to PCl3 and Cl2.
- Oxidation states:
- Chlorine changes from -1 to 0 (oxidation).
- Phosphorus changes from +5 to +3 (reduction).
- Conclusion: Both oxidation and reduction occur, so this is a redox reaction.

6. **Final Conclusion**:
- The first reaction (chromate reaction) does not involve any change in oxidation states, hence it is not a redox reaction. The other three reactions involve changes in oxidation states, confirming they are redox reactions.

### Answer:
The reaction that does not represent a redox reaction is the **first option (chromate reaction)**.

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