Which of the following are redox reaction ?

Options

A. `BaCl_2 +H_2SO_4 rarr BaSO_4 +2HCl`
B. `Zn+2HCl rarr ZnCl_2 +H_2`
C. `6CO_2+6H_2O rarr C_6H_(12)O_6+6O_2`
D. `KCN +AgCN rarrK[Ag(CN)_2]`

Answer

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) and reduction (gain of electrons) occurring simultaneously.

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions labeled A, B, C, and D. We will analyze each one.

2. **Analyze Reaction A**:
- Reaction: BACl + H2SO4 → BSO4 + 2HCl
- Oxidation states:
- Barium (Ba) remains +2 in both reactants and products.
- Chlorine (Cl) remains -1 in both reactants and products.
- Sulfur (S) remains +6 in both reactants and products.
- Hydrogen (H) remains +1 in both reactants and products.
- Oxygen (O) remains -2 in both reactants and products.
- Conclusion: No change in oxidation states; therefore, **not a redox reaction**.

3. **Analyze Reaction B**:
- Reaction: Zn + 2HCl → ZnCl2 + H2
- Oxidation states:
- Zinc (Zn) changes from 0 (elemental) to +2 (in ZnCl2) → **oxidation**.
- Hydrogen (H) changes from +1 (in HCl) to 0 (in H2) → **reduction**.
- Conclusion: Both oxidation and reduction occur; therefore, **this is a redox reaction**.

4. **Analyze Reaction C**:
- Reaction: C + O2 → CO2
- Oxidation states:
- Carbon (C) changes from +4 (in CO2) to 0 (elemental) → **reduction**.
- Oxygen (O) changes from -2 (in O2) to 0 (elemental) → **oxidation**.
- Conclusion: Both oxidation and reduction occur; therefore, **this is a redox reaction**.

5. **Analyze Reaction D**:
- Reaction: KCN + AgCN → KAgCN2
- Oxidation states:
- Potassium (K) remains +1 in both reactants and products.
- Cyanide (CN) remains -1 in both reactants and products.
- Silver (Ag) remains +1 in both reactants and products.
- Conclusion: No change in oxidation states; therefore, **not a redox reaction**.

### Final Answer:
The reactions that are redox reactions are **B and C**.