Which of the following ions has the maximum magnetic moment in aqueous solution ?

Answer

To determine which ion has the maximum magnetic moment in aqueous solution, we need to analyze the number of unpaired electrons in each ion. The magnetic moment (μ) can be calculated using the formula:

\[ \mu = \sqrt{n(n + 2)} \text{ Bohr magneton} \]

where \( n \) is the number of unpaired electrons. The more unpaired electrons an ion has, the greater its magnetic moment will be.

### Step-by-Step Solution:

1. **Identify the Ions**: We will consider the following ions:
- Fe²⁺
- Ti²⁺
- Mn²⁺
- Cr²⁺

2. **Determine the Electronic Configurations**:
- **Fe²⁺**: The atomic number of Fe is 26. The electronic configuration of Fe is [Ar] 3d⁶ 4s². For Fe²⁺, we remove two electrons from the 4s orbital, resulting in 3d⁶.
- **Ti²⁺**: The atomic number of Ti is 22. The electronic configuration of Ti is [Ar] 3d² 4s². For Ti²⁺, we remove two electrons from the 4s orbital, resulting in 3d².
- **Mn²⁺**: The atomic number of Mn is 25. The electronic configuration of Mn is [Ar] 3d⁵ 4s². For Mn²⁺, we remove two electrons from the 4s orbital, resulting in 3d⁵.
- **Cr²⁺**: The atomic number of Cr is 24. The electronic configuration of Cr is [Ar] 3d⁵ 4s¹ (due to stability of half-filled orbitals). For Cr²⁺, we remove one electron from the 4s and one from the 3d, resulting in 3d⁴.

3. **Count the Number of Unpaired Electrons**:
- **Fe²⁺ (3d⁶)**: The configuration can be represented as ↑↓ ↑ ↑ ↑ ↑ (4 unpaired electrons).
- **Ti²⁺ (3d²)**: The configuration can be represented as ↑ ↑ (2 unpaired electrons).
- **Mn²⁺ (3d⁵)**: The configuration can be represented as ↑ ↑ ↑ ↑ ↑ (5 unpaired electrons).
- **Cr²⁺ (3d⁴)**: The configuration can be represented as ↑ ↑ ↑ ↑ (4 unpaired electrons).

4. **Identify the Ion with Maximum Unpaired Electrons**:
- Fe²⁺: 4 unpaired electrons
- Ti²⁺: 2 unpaired electrons
- Mn²⁺: 5 unpaired electrons
- Cr²⁺: 4 unpaired electrons

From the above analysis, Mn²⁺ has the maximum number of unpaired electrons (5).

5. **Conclusion**:
The ion with the maximum magnetic moment in aqueous solution is **Mn²⁺**.

### Final Answer:
**C. Mn²⁺ has the maximum magnetic moment in aqueous solution.**