Electrode potential of `M^(2+)//M` for Ni is abnormal because of

Options

A. High `IE_(1)+IE_(2)`
B. High hydration energy
C. `DeltaH_("atomisation")`
D. Electronic configuration of `Ni^(2+)`

Answer

To solve the question regarding why the electrode potential of `M^(2+)//M` for nickel (Ni) is abnormal, we can break it down into several steps:

### Step-by-Step Solution:

1. **Understanding Electrode Potential**:
- The electrode potential of a metal ion (like `Ni^(2+)`) refers to its tendency to gain or lose electrons when in contact with its solid metal form (Ni). A higher potential indicates a greater tendency to gain electrons (be reduced), while a lower potential indicates a tendency to lose electrons (be oxidized).

2. **Identifying the Factors Affecting Electrode Potential**:
- The electrode potential can be influenced by several factors, including ionization enthalpy, hydration energy, and the electronic configuration of the metal ion.

3. **High Ionization Enthalpy**:
- Nickel has a relatively high ionization enthalpy, which means it requires a significant amount of energy to remove electrons from the Ni atom. This contributes to the stability of the Ni atom compared to its ion.

4. **High Hydration Energy**:
- The hydration energy is the energy released when ions are solvated by water molecules. For `Ni^(2+)`, due to its small ionic size, the hydration energy is highly negative. This means that when `Ni^(2+)` ions are surrounded by water molecules, a considerable amount of energy is released, making the ion more stable in solution.

5. **Effect of Hydration Energy on Electrode Potential**:
- The high negative hydration energy implies that `Ni^(2+)` ions are stabilized in aqueous solution, making it less likely for them to lose electrons (oxidize) and more likely to gain electrons (reduce). This results in an abnormal electrode potential, as the ion does not behave as expected based on its position in the periodic table.

6. **Electronic Configuration of Nickel**:
- The electronic configuration of `Ni` is `[Ar] 3d^8 4s^2`. When it loses two electrons to form `Ni^(2+)`, it becomes `[Ar] 3d^8`. The stability of the `3d` subshell also contributes to the unusual behavior of `Ni^(2+)`.

7. **Conclusion**:
- The abnormal electrode potential of `Ni^(2+)//Ni` is primarily due to its high negative hydration energy, which stabilizes the ion and affects its ability to lose electrons.

### Final Answer:
The electrode potential of `M^(2+)//M` for nickel is abnormal because of its high negative hydration energy, which stabilizes the `Ni^(2+)` ion in solution and affects its reduction potential.