Which of the following is are redox reaction(s) ?

Options

A. `BaO_(2)+H_(2)SO_(4)toBaSO_(4)+H_(2)O_(2)`
B. `2BaO+O_(2)to2BaO_(2)`
C. `2kClO_(3)to2kCl+3O_(2)`
D. `SO_(2)+2H_(2)Sto2H_(2)O+3S`

Explanation

To determine which of the given reactions are redox reactions, we need to analyze the oxidation states of the elements involved in each reaction. A redox reaction involves both oxidation (loss of electrons/increase in oxidation state) and reduction (gain of electrons/decrease in oxidation state).

### Step-by-Step Solution:

1. **Identify the Reactions**: The reactions given are:
- A: BaO2 + H2SO4 → BaSO4 + H2O2
- B: KClO3 → KCl + O2
- C: SO2 + H2S → S + H2O
- D: H2 + Cl2 → 2HCl

2. **Analyze Reaction A**:
- In BaO2, Ba is +2, O is -2.
- In H2SO4, H is +1, S is +6, O is -2.
- In BaSO4, Ba is +2, S is +6, O is -2.
- In H2O2, H is +1, O is -1.
- **Oxidation States**:
- Ba: +2 (no change)
- S: +6 (no change)
- O: -2 in BaO2 to -1 in H2O2 (increase in oxidation state)
- **Conclusion**: No change in oxidation state for Ba and S, so this is **not a redox reaction**.

3. **Analyze Reaction B**:
- In KClO3, K is +1, Cl is +5, O is -2.
- In KCl, K is +1, Cl is -1.
- **Oxidation States**:
- Cl: +5 to -1 (decrease in oxidation state, reduction)
- O: -2 to 0 (increase in oxidation state, oxidation)
- **Conclusion**: Both oxidation and reduction occur, so this is a **redox reaction**.

4. **Analyze Reaction C**:
- In SO2, S is +4, O is -2.
- In H2S, H is +1, S is -2.
- In elemental S, S is 0.
- In H2O, H is +1, O is -2.
- **Oxidation States**:
- S: +4 to 0 (decrease in oxidation state, reduction)
- S: -2 to 0 (increase in oxidation state, oxidation)
- **Conclusion**: Both oxidation and reduction occur, so this is a **redox reaction**.

5. **Analyze Reaction D**:
- In H2, H is 0.
- In Cl2, Cl is 0.
- In 2HCl, H is +1, Cl is -1.
- **Oxidation States**:
- H: 0 to +1 (increase in oxidation state, oxidation)
- Cl: 0 to -1 (decrease in oxidation state, reduction)
- **Conclusion**: Both oxidation and reduction occur, so this is a **redox reaction**.

### Final Answer:
The reactions that are redox reactions are:
- B: KClO3 → KCl + O2
- C: SO2 + H2S → S + H2O
- D: H2 + Cl2 → 2HCl

### Summary:
- **A**: Not a redox reaction.
- **B**: Redox reaction.
- **C**: Redox reaction.
- **D**: Redox reaction.