In which of the following salt bridge is not needed ?

Options

A. `Pb|PbSO_(4)(s)|H_(2)SO_(4)|PbO_(2)(s)|Pb`
B. `Cd|CdO(s)|KOH(aq)|NiO_(2)(s)|Ni`
C. `Fe(s)|FeO(s)|KOH(aq),Ni_(2)O_(3)(s)|Ni`
D. `Zn|ZnSO_(4)|CuSO_(4)|Cu`

Explanation

To determine in which of the following cases a salt bridge is not needed, we need to analyze each option based on the presence of electrolytes in the half-cells. A salt bridge is typically used to maintain electrical neutrality by allowing ions to flow between the two half-cells in an electrochemical cell. If either half-cell lacks an electrolyte, a salt bridge is not necessary.

### Step-by-Step Solution:

1. **Understanding the Function of a Salt Bridge:**
- A salt bridge connects the two half-cells of an electrochemical cell, allowing ions to flow and maintain charge balance. If one of the half-cells does not contain an electrolyte, a salt bridge is not required.

2. **Analyzing Each Option:**
- **Option A: Lead and Lead Sulfate**
- In this case, Lead Sulfate is in solid form, and Lead (Pb) is a metal. Since there is no liquid electrolyte present in this half-cell, a salt bridge is not needed.

- **Option B: Cadmium and Cadmium Oxide**
- Here, Cadmium Oxide is also a solid, and Cadmium (Cd) is a metal. Similar to the previous case, there is no liquid electrolyte, so a salt bridge is not necessary.

- **Option C: Ferrous and Ferric Oxide**
- In this half-cell, both Ferrous (Fe²⁺) and Ferric Oxide (Fe₂O₃) are not in a liquid state. Therefore, there is no electrolyte present, and a salt bridge is not required.

- **Option D: Zinc and Zinc Sulfate, Copper and Copper Sulfate**
- In this case, Zinc Sulfate (ZnSO₄) and Copper Sulfate (CuSO₄) are both electrolytes in their respective half-cells. Therefore, a salt bridge is necessary to maintain electrical neutrality between the two half-cells.

3. **Conclusion:**
- The options that do not require a salt bridge are A (Lead and Lead Sulfate), B (Cadmium and Cadmium Oxide), and C (Ferrous and Ferric Oxide). Option D requires a salt bridge.

### Final Answer:
The salt bridge is not needed in options A, B, and C.