Which of the following involves redox reaction?

Options

A. Decomposition of `CaCO_(3)`
B. Rusting
C. Reaction of NaOH with HCl
D. `Zn rarr Zn^(++)+2e^(-)`

Answer

To determine which of the given options involves a redox reaction, we need to analyze each option based on the definitions of oxidation and reduction. 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, leading to changes in their oxidation states. Oxidation is the loss of electrons, while reduction is the gain of electrons.

2. **Analyzing Each Option**:
- **Option 1: Decomposition of Calcium Carbonate (CaCO₃)**:
- When heated, CaCO₃ decomposes into CaO and CO₂.
- Oxidation states:
- In CaCO₃: Ca is +2, C is +4, O is -2.
- In CaO: Ca is +2, O is -2.
- In CO₂: C is +4, O is -2.
- There is no change in oxidation states for Ca, C, or O during the reaction.
- **Conclusion**: No redox reaction occurs here.

- **Option 2: Rusting of Iron**:
- Rusting involves the reaction of iron with oxygen and moisture to form iron(III) oxide (Fe₂O₃).
- Oxidation states:
- Fe²⁺ (oxidation state +2) to Fe³⁺ (oxidation state +3) indicates oxidation (loss of electrons).
- O₂ (oxidation state 0) to O²⁻ (oxidation state -2) indicates reduction (gain of electrons).
- **Conclusion**: Both oxidation and reduction occur, so this is a redox reaction.

- **Option 3: Reaction of NaOH with HCl**:
- This reaction produces NaCl and water.
- Oxidation states:
- Na is +1, Cl is -1, O is -2, H is +1 in both reactants and products.
- There is no change in oxidation states.
- **Conclusion**: No redox reaction occurs here.

- **Option 4: Zinc Losing Electrons**:
- Zinc (Zn) loses 2 electrons to form Zn²⁺.
- This indicates oxidation (loss of electrons).
- However, there is no corresponding reduction occurring in this scenario.
- **Conclusion**: This is not a redox reaction since only oxidation is present.

3. **Final Conclusion**:
- The only option that involves a redox reaction is **Option 2: Rusting of Iron**.

### Answer:
The correct answer is **Option 2: Rusting of Iron**.