Which of the following represents a redox reaction?

Options

A. `NaOH+HClrarrNaCl+H_(2)O`
B. `BaCl_(2)+H_(2)SO_(4)rarrBaSO_(4)+2HCl`
C. `CuSO_(4)+2H_(2)OrarrCu(OH)_(2)+H_(2)SO_(4)`
D. `Zn+2HClrarrZnCl_(2)+H_(2)`

Explanation

To determine which of the given reactions represents a redox reaction, we need to analyze each option to see if oxidation and reduction are occurring simultaneously. A redox reaction involves the transfer of electrons, where one species is oxidized (loses electrons) and another is reduced (gains electrons).

### Step-by-Step Solution:

1. **Identify the Reactions**:
- The question presents several reactions. We need to analyze each one to see if they involve changes in oxidation states.

2. **Analyze Reaction 1: NaOH + HCl → NaCl + H2O**:
- This is a neutralization reaction between an acid (HCl) and a base (NaOH) to form salt (NaCl) and water (H2O).
- **Oxidation States**: Na remains +1, O remains -2, H remains +1, Cl remains -1. No change in oxidation states.
- **Conclusion**: Not a redox reaction.

3. **Analyze Reaction 2: BaCl2 + H2SO4 → BaSO4 + 2HCl**:
- This is also a neutralization reaction, where barium chloride reacts with sulfuric acid to form barium sulfate and hydrochloric acid.
- **Oxidation States**: Ba remains +2, Cl remains -1, S remains +6, O remains -2. No change in oxidation states.
- **Conclusion**: Not a redox reaction.

4. **Analyze Reaction 3: CuSO4 + 2H2O → Cu(OH)2 + H2SO4**:
- This reaction involves copper sulfate reacting with water to form copper hydroxide and sulfuric acid.
- **Oxidation States**: Cu remains +2 in both reactants and products. No change in oxidation states.
- **Conclusion**: Not a redox reaction.

5. **Analyze Reaction 4: Zn + 2HCl → ZnCl2 + H2**:
- Here, zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
- **Oxidation States**:
- Zn goes from 0 (elemental) to +2 (in ZnCl2), indicating oxidation (loss of electrons).
- H goes from +1 (in HCl) to 0 (in H2), indicating reduction (gain of electrons).
- **Conclusion**: This is a redox reaction because oxidation and reduction are occurring simultaneously.

6. **Final Answer**: The correct option that represents a redox reaction is **Zn + 2HCl → ZnCl2 + H2**.