Which of the following reactions canot be a base for electrochemical cell?

Options

A. `H_2+O_2 to H_2O`
B. `AgNO_3 + Zn to Zn(NO_3)_2 + Ag`
C. `AgNO_3 + NaCl to AgCl darr + NaNO_3`
D. `KMnO_4 + FeSO_4 + H_2SO_4 to K_2SO_4 + Fe_2(SO_4)_3 + MnSO_4 + H_2O`

Explanation

To determine which of the given reactions cannot serve as a basis for an electrochemical cell, we need to identify whether each reaction is a redox reaction. A redox reaction involves the simultaneous oxidation and reduction of substances. Let's analyze each option step by step.

### Step 1: Analyze the First Reaction
**Reaction:** H₂ + O₂ → H₂O

- **Oxidation States:**
- H₂: 0 (elemental form)
- O₂: 0 (elemental form)
- H₂O: H = +1, O = -2

- **Changes:**
- H goes from 0 to +1 (oxidation)
- O goes from 0 to -2 (reduction)

**Conclusion:** This is a redox reaction.

### Step 2: Analyze the Second Reaction
**Reaction:** AgNO₃ + Zn → Zn(NO₃)₂ + Ag

- **Oxidation States:**
- Ag in AgNO₃: +1
- Zn: 0
- Zn(NO₃)₂: Zn = +2, Ag = 0

- **Changes:**
- Ag goes from +1 to 0 (reduction)
- Zn goes from 0 to +2 (oxidation)

**Conclusion:** This is also a redox reaction.

### Step 3: Analyze the Third Reaction
**Reaction:** AgNO₃ + NaCl → AgCl + NaNO₃

- **Oxidation States:**
- Ag in AgNO₃: +1
- Na in NaCl: +1
- AgCl: Ag = +1, NaNO₃: Na = +1

- **Changes:**
- There is no change in the oxidation states of Ag and Na.

**Conclusion:** This is NOT a redox reaction.

### Step 4: Analyze the Fourth Reaction
**Reaction:** KMnO₄ + FeSO₄ + H₂SO₄ → K₂SO₄ + Fe₂(SO₄)₃ + MnSO₄ + H₂SO₄

- **Oxidation States:**
- Mn in KMnO₄: +7
- Fe in FeSO₄: +2
- K₂SO₄: K = +1, Fe₂(SO₄)₃: Fe = +3, MnSO₄: Mn = +2

- **Changes:**
- Mn goes from +7 to +2 (reduction)
- Fe goes from +2 to +3 (oxidation)

**Conclusion:** This is a redox reaction.

### Final Conclusion
Among the reactions analyzed:
- **First Reaction:** Redox reaction
- **Second Reaction:** Redox reaction
- **Third Reaction:** NOT a redox reaction (cannot be a basis for an electrochemical cell)
- **Fourth Reaction:** Redox reaction

Thus, the reaction that cannot serve as a basis for an electrochemical cell is the **third reaction (AgNO₃ + NaCl → AgCl + NaNO₃)**.

### Answer:
**The reaction that cannot be a base for an electrochemical cell is the third reaction (AgNO₃ + NaCl → AgCl + NaNO₃).**

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