The pair of ions which do not have same number of unpaired electrons is

Options

A. `Mn^(2+) and Fe^(3+)`
B. `Ti^(2+) and Ni^(2+)`
C. `Cu^(2+) and Ti^(3+)`
D. `Fe^(2+) and Ni^(2+)`

Answer

To determine the pair of ions that do not have the same number of unpaired electrons, we will analyze the electronic configurations of each ion provided in the options.

### Step-by-Step Solution:

1. **Identify the Ions**: The pairs of ions given are:
- (a) Mn²⁺ and Fe²⁺
- (b) Ti²⁺ and Ni²⁺
- (c) Cu²⁺ and Ti³⁺
- (d) Fe²⁺ and Ni²⁺

2. **Determine Electronic Configurations**:
- **Mn²⁺**: The atomic number of manganese (Mn) is 25. Its electronic configuration is [Ar] 4s² 3d⁵. For Mn²⁺, we remove two electrons (from 4s), giving us [Ar] 3d⁵.
- **Fe²⁺**: The atomic number of iron (Fe) is 26. Its electronic configuration is [Ar] 4s² 3d⁶. For Fe²⁺, we remove two electrons (from 4s), giving us [Ar] 3d⁶.
- **Ti²⁺**: The atomic number of titanium (Ti) is 22. Its electronic configuration is [Ar] 4s² 3d². For Ti²⁺, we remove two electrons (from 4s), giving us [Ar] 3d².
- **Ni²⁺**: The atomic number of nickel (Ni) is 28. Its electronic configuration is [Ar] 4s² 3d⁸. For Ni²⁺, we remove two electrons (from 4s), giving us [Ar] 3d⁸.
- **Cu²⁺**: The atomic number of copper (Cu) is 29. Its electronic configuration is [Ar] 4s² 3d¹⁰. For Cu²⁺, we remove two electrons (from 4s), giving us [Ar] 3d⁹.
- **Ti³⁺**: For Ti³⁺, we remove three electrons from Ti, giving us [Ar] 3d¹.

3. **Count Unpaired Electrons**:
- **Mn²⁺** ([Ar] 3d⁵): 5 unpaired electrons (all five 3d electrons are unpaired).
- **Fe²⁺** ([Ar] 3d⁶): 4 unpaired electrons (three 3d electrons are unpaired, and two are paired).
- **Ti²⁺** ([Ar] 3d²): 2 unpaired electrons (two 3d electrons are unpaired).
- **Ni²⁺** ([Ar] 3d⁸): 2 unpaired electrons (two 3d electrons are unpaired).
- **Cu²⁺** ([Ar] 3d⁹): 1 unpaired electron (one 3d electron is unpaired).
- **Ti³⁺** ([Ar] 3d¹): 1 unpaired electron (one 3d electron is unpaired).

4. **Compare Unpaired Electrons**:
- (a) Mn²⁺ (5 unpaired) and Fe²⁺ (4 unpaired) → Different
- (b) Ti²⁺ (2 unpaired) and Ni²⁺ (2 unpaired) → Same
- (c) Cu²⁺ (1 unpaired) and Ti³⁺ (1 unpaired) → Same
- (d) Fe²⁺ (4 unpaired) and Ni²⁺ (2 unpaired) → Different

5. **Conclusion**: The pair of ions that do not have the same number of unpaired electrons is **Fe²⁺ and Ni²⁺** (option d).

### Final Answer:
The pair of ions which do not have the same number of unpaired electrons is **Fe²⁺ and Ni²⁺**.