Which of the following reactions involve oxidation and reduction?

Options

A. `NaBr+HCl rarr NaCl+HBr`
B. `HBr+AgNO_(3) rarr AgBr+HNO_(3)`
C. `H_(2)+Br_(2) rarr 2HBr`
D. `Na_(2)O+H_(2)SO_(4) rarr Na_(2)SO_(4)+H_(2)O`

Answer

To determine which of the given reactions involve oxidation and reduction, we need to analyze the changes in oxidation states of the elements involved in each reaction. Oxidation is defined as the loss of electrons (increase in oxidation state), while reduction is the gain of electrons (decrease in oxidation state).

### Step-by-Step Solution:

1. **Identify the Reactions**: We need to analyze each of the given reactions to check for changes in oxidation states.

2. **Analyze Reaction 1: NaBr + HCl → NaCl + HBr**
- Oxidation States:
- Na: +1
- Br: -1
- H: +1
- Cl: -1
- Products:
- NaCl: Na: +1, Cl: -1
- HBr: H: +1, Br: -1
- **Conclusion**: No change in oxidation states for any element. Therefore, this reaction does not involve oxidation or reduction.

3. **Analyze Reaction 2: HBr + AgNO3 → AgBr + HNO3**
- Oxidation States:
- H: +1, Br: -1 (in HBr)
- Ag: +1 (in AgNO3), N: +5, O: -2 (in NO3^-)
- Products:
- AgBr: Ag: +1, Br: -1
- HNO3: H: +1, N: +5, O: -2
- **Conclusion**: No change in oxidation states for any element. Therefore, this reaction does not involve oxidation or reduction.

4. **Analyze Reaction 3: H2 + Br2 → 2HBr**
- Oxidation States:
- H: 0 (in H2), Br: 0 (in Br2)
- Products:
- HBr: H: +1, Br: -1
- **Conclusion**:
- H changes from 0 to +1 (oxidation).
- Br changes from 0 to -1 (reduction).
- This reaction involves both oxidation and reduction.

5. **Analyze Reaction 4: Na2O + H2SO4 → Na2SO4 + H2O**
- Oxidation States:
- Na: +1 (in Na2O), O: -2
- H: +1, S: +6, O: -2 (in H2SO4)
- Products:
- Na2SO4: Na: +1, S: +6, O: -2
- H2O: H: +1, O: -2
- **Conclusion**: No change in oxidation states for any element. Therefore, this reaction does not involve oxidation or reduction.

### Final Answer:
The only reaction that involves both oxidation and reduction is **Reaction 3: H2 + Br2 → 2HBr**.

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