Which of the following is a redox decomposition reaction ?

Options

A. `CaCO_(3)(s)overset(Delta)toCaO(s)+CO_(2)(g)`
B. `2KClO_(3)(s)overset(Delta)to2KCl(s)+3O_(2)(g)`
C. `2H_(2)O(l)+2F_(2)(g)to4HF(aq)+O_(2)(g)`
D. `2Na(s)+Cl_(2)(g)to2NaCl(s)`

Answer

To determine which of the given reactions is a redox decomposition reaction, we need to analyze each reaction based on the definitions of redox and decomposition reactions.

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Redox Reaction**: A reaction that involves a change in oxidation states of the reactants, indicating that oxidation (loss of electrons) and reduction (gain of electrons) are occurring.
- **Decomposition Reaction**: A reaction where one reactant breaks down into two or more products.

2. **Analyze Each Reaction**:
- **Reaction A**: \( \text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g) \)
- Oxidation states:
- Ca: +2 (remains +2)
- C: +4 (remains +4)
- No change in oxidation states; therefore, it is not a redox reaction.
- This is a decomposition reaction, but not a redox decomposition.

- **Reaction B**: \( \text{KClO}_3 (s) \rightarrow 2 \text{KCl} + 3 \text{O}_2 \)
- Oxidation states:
- Cl in KClO3: +5
- Cl in KCl: -1
- There is a change in oxidation state (from +5 to -1), indicating it is a redox reaction.
- One reactant (KClO3) decomposes into multiple products (KCl and O2), confirming it is a decomposition reaction as well.

- **Reaction C**: \( 2 \text{H}_2\text{O} (l) + 2 \text{HF}_2 \rightarrow 4 \text{HF} + \text{O}_2 \)
- Oxidation states:
- H in H2O: +1 (remains +1)
- O in H2O: -2 (remains -2)
- H in HF: +1 (remains +1)
- O in O2: 0 (remains 0)
- No change in oxidation states; therefore, it is not a redox reaction.
- This is not a decomposition reaction either.

- **Reaction D**: \( 2 \text{Na} (s) + \text{Cl}_2 (g) \rightarrow 2 \text{NaCl} (s) \)
- Oxidation states:
- Na: 0 (in elemental form) to +1 (in NaCl)
- Cl: 0 (in elemental form) to -1 (in NaCl)
- There is a change in oxidation states, indicating it is a redox reaction.
- However, it is not a decomposition reaction since it involves two reactants forming one product.

3. **Conclusion**:
- The only reaction that is both a redox and a decomposition reaction is **Reaction B**: \( \text{KClO}_3 (s) \rightarrow 2 \text{KCl} + 3 \text{O}_2 \).

### Final Answer:
**Option B: \( \text{KClO}_3 (s) \rightarrow 2 \text{KCl} + 3 \text{O}_2 \)** is a redox decomposition reaction.