Among the following pairs of ions, the lower oxidation state in aqueous solution is more stable than the other,in:

Options

A. `Zn^(2+),Zn^(3+)`
B. `Cu^(+),Cu^(2+)`
C. `Cr^(2+),Cr^(3+)`
D. `V^(3+)`,`V^(5+)`

Answer

To determine which pair of ions has the lower oxidation state that is more stable in aqueous solution, we will analyze each pair based on their electronic configurations and stability considerations.

### Step-by-Step Solution:

1. **Identify the pairs of ions**: The question presents four pairs of ions. We need to analyze each pair:
- Pair 1: Zn²⁺ and Zn³⁺
- Pair 2: Cu⁺ and Cu²⁺
- Pair 3: Cr²⁺ and Cr³⁺
- Pair 4: V³⁺ and V⁵⁺

2. **Analyze Pair 1: Zn²⁺ and Zn³⁺**:
- **Zn²⁺**: Electronic configuration is [Ar] 3d¹⁰ 4s⁰ (completely filled d-orbital).
- **Zn³⁺**: Electronic configuration is [Ar] 3d⁹ 4s⁰ (one electron removed from a filled d-orbital).
- **Stability**: Zn²⁺ is more stable due to its completely filled d-orbital, while Zn³⁺ is less stable because it has a half-filled d-orbital which is less stable.

3. **Analyze Pair 2: Cu⁺ and Cu²⁺**:
- **Cu⁺**: Electronic configuration is [Ar] 3d¹⁰ 4s⁰ (completely filled d-orbital).
- **Cu²⁺**: Electronic configuration is [Ar] 3d⁹ 4s⁰ (one electron removed from a filled d-orbital).
- **Stability**: Although Cu⁺ appears stable, in aqueous solution, it tends to disproportionate to Cu²⁺ and Cu(s) due to the high hydration energy of Cu²⁺. Therefore, Cu²⁺ is more stable in aqueous solution.

4. **Analyze Pair 3: Cr²⁺ and Cr³⁺**:
- **Cr²⁺**: Electronic configuration is [Ar] 3d⁴ 4s⁰.
- **Cr³⁺**: Electronic configuration is [Ar] 3d³ 4s⁰.
- **Stability**: Cr³⁺ is more stable due to the half-filled t₂g orbitals in an octahedral field, making it exceptionally stable. Thus, Cr²⁺ is less stable compared to Cr³⁺.

5. **Analyze Pair 4: V³⁺ and V⁵⁺**:
- **V³⁺**: Electronic configuration is [Ar] 3d² 4s⁰.
- **V⁵⁺**: Electronic configuration is [Ar] 3d⁰ 4s⁰ (noble gas configuration).
- **Stability**: V⁵⁺ is highly stable due to achieving a noble gas configuration, while V³⁺ is less stable as it tends to lose more electrons to reach V⁵⁺.

6. **Conclusion**:
- Among the pairs analyzed, **Zn²⁺ and Zn³⁺** is the only pair where the lower oxidation state (Zn²⁺) is more stable than the higher oxidation state (Zn³⁺). Therefore, the answer to the question is Pair 1: Zn²⁺ is more stable than Zn³⁺ in aqueous solution.

### Final Answer:
The correct pair is **Zn²⁺ and Zn³⁺**, where Zn²⁺ is the more stable lower oxidation state in aqueous solution.