Which of the following aquated metal ions has the highest paramagnetism?

Options

A. `[Cr(H_(2)O)_(6)]^(3+)`
B. `[Fe(H_(2)O)_(6)]^(2+)`
C. `[Cu(H_(2)O)_(6)]^(3+)`
D. `[Zn(H_(2)O)_(2)]^(2+)`

Answer

To determine which of the given aquated metal ions has the highest paramagnetism, we need to analyze the electronic configurations of the metal ions in their respective oxidation states and count the number of unpaired electrons. The more unpaired electrons a species has, the more paramagnetic it is.

### Step-by-Step Solution:

1. **Identify the Metal Ions and Their Oxidation States:**
- For the first complex, Cr(H2O)6, the oxidation state of chromium (Cr) can be calculated as follows:
\[ X + 0 \times 6 = 0 \quad \Rightarrow \quad X = +3 \]
- For the second complex, Fe(H2O)6, the oxidation state of iron (Fe) is:
\[ X + 0 \times 6 = +2 \quad \Rightarrow \quad X = +2 \]
- For the third complex, Cu(H2O)6, the oxidation state of copper (Cu) is:
\[ X + 0 \times 6 = +3 \quad \Rightarrow \quad X = +3 \]
- For the fourth complex, Zn(H2O)6, the oxidation state of zinc (Zn) is:
\[ X + 0 \times 6 = +2 \quad \Rightarrow \quad X = +2 \]

2. **Write the Electronic Configurations:**
- **Chromium (Cr) +3:**
- Atomic number of Cr = 24
- Ground state configuration: [Ar] 4s² 3d⁴
- For Cr³⁺: [Ar] 3d³ (3 unpaired electrons)

- **Iron (Fe) +2:**
- Atomic number of Fe = 26
- Ground state configuration: [Ar] 4s² 3d⁶
- For Fe²⁺: [Ar] 3d⁶ (4 unpaired electrons)

- **Copper (Cu) +3:**
- Atomic number of Cu = 29
- Ground state configuration: [Ar] 4s¹ 3d¹⁰
- For Cu³⁺: [Ar] 3d⁹ (1 unpaired electron)

- **Zinc (Zn) +2:**
- Atomic number of Zn = 30
- Ground state configuration: [Ar] 4s² 3d¹⁰
- For Zn²⁺: [Ar] 3d¹⁰ (0 unpaired electrons)

3. **Count the Number of Unpaired Electrons:**
- Cr³⁺: 3 unpaired electrons
- Fe²⁺: 4 unpaired electrons
- Cu³⁺: 1 unpaired electron
- Zn²⁺: 0 unpaired electrons

4. **Determine the Metal Ion with the Highest Paramagnetism:**
- The metal ion with the highest number of unpaired electrons is Fe²⁺ with 4 unpaired electrons.

### Conclusion:
The aquated metal ion with the highest paramagnetism is **Fe²⁺** from the complex Fe(H2O)6.