Among the following ions which one has the highest paramagnetism?

Options

A. (a) `[Cr(H_2O)_6]^(3+)`
B. (b) `[Cu(H_2O)_6]^(2+)`
C. (c) `[Fe(H_2O)_6]^(2+)`
D. (d) `[Zn(H_2O)_6]^(2+)`

Explanation

To determine which ion has the highest paramagnetism among the given options (Chromium +3, Copper +2, Iron +2, and Zinc +2), we need to analyze the number of unpaired electrons in each ion. Paramagnetism is directly related to the presence of unpaired electrons in the d-orbitals of transition metals.

### Step-by-Step Solution:

1. **Identify the oxidation states and electronic configurations:**
- Chromium (Cr) has an atomic number of 24. In the +3 oxidation state, its electronic configuration is:
- Cr: [Ar] 3d^5 4s^1 → Cr^3+: [Ar] 3d^3
- Copper (Cu) has an atomic number of 29. In the +2 oxidation state, its electronic configuration is:
- Cu: [Ar] 3d^10 4s^1 → Cu^2+: [Ar] 3d^9
- Iron (Fe) has an atomic number of 26. In the +2 oxidation state, its electronic configuration is:
- Fe: [Ar] 3d^6 4s^2 → Fe^2+: [Ar] 3d^6
- Zinc (Zn) has an atomic number of 30. In the +2 oxidation state, its electronic configuration is:
- Zn: [Ar] 3d^10 4s^2 → Zn^2+: [Ar] 3d^10

2. **Count the number of unpaired electrons:**
- For Cr^3+ (3d^3):
- There are 3 unpaired electrons (one in each of the three 3d orbitals).
- For Cu^2+ (3d^9):
- There is 1 unpaired electron (the 9th electron occupies one of the 3d orbitals).
- For Fe^2+ (3d^6):
- There are 4 unpaired electrons (the 6 electrons fill the orbitals with 4 remaining unpaired).
- For Zn^2+ (3d^10):
- There are 0 unpaired electrons (all d-orbitals are fully filled).

3. **Determine the ion with the highest number of unpaired electrons:**
- Cr^3+: 3 unpaired electrons
- Cu^2+: 1 unpaired electron
- Fe^2+: 4 unpaired electrons
- Zn^2+: 0 unpaired electrons

4. **Conclusion:**
- The ion with the highest paramagnetism is **Fe^2+** because it has the most unpaired electrons (4 unpaired electrons).

### Final Answer:
**Iron (Fe^2+) has the highest paramagnetism among the given ions.**

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