Amongst the following the lowest degree of paramagnetism per mole of the compound at `298K` will be shown by:

Options

A. `MnSO_(4).4H_(2)O`
B. `CuSO_(4).5H_(2)O`
C. `FeSO_(4).6H_(2)O`
D. `NiSO_(4).6H_(2)O`

Answer

To determine which compound exhibits the lowest degree of paramagnetism at 298 K among the given options, we need to analyze the number of unpaired electrons in each compound. The presence of unpaired electrons contributes to paramagnetism, with more unpaired electrons resulting in greater paramagnetic behavior.

### Step-by-Step Solution:

1. **Understanding Paramagnetism**:
- Paramagnetism arises from the presence of unpaired electrons in the electronic configuration of an atom or ion. The more unpaired electrons present, the stronger the paramagnetism.

2. **Identify the Compounds**:
- The compounds given are:
1. MnSO4 · 4H2O
2. CuSO4 · 5H2O
3. FeSO4 · 6H2O
4. NiSO4 · 6H2O

3. **Determine the Oxidation States and Electronic Configurations**:
- **MnSO4 · 4H2O**: Manganese (Mn) is in the +2 oxidation state.
- Electronic configuration: Mn²⁺ → [Ar] 3d⁵ 4s⁰
- Unpaired electrons: 5 (all 5 electrons in 3d subshell are unpaired)

- **CuSO4 · 5H2O**: Copper (Cu) is in the +2 oxidation state.
- Electronic configuration: Cu²⁺ → [Ar] 3d⁹ 4s⁰
- Unpaired electrons: 1 (the 3d subshell has 1 unpaired electron)

- **FeSO4 · 6H2O**: Iron (Fe) is in the +2 oxidation state.
- Electronic configuration: Fe²⁺ → [Ar] 3d⁶ 4s⁰
- Unpaired electrons: 4 (the 3d subshell has 4 unpaired electrons)

- **NiSO4 · 6H2O**: Nickel (Ni) is in the +2 oxidation state.
- Electronic configuration: Ni²⁺ → [Ar] 3d⁸ 4s⁰
- Unpaired electrons: 2 (the 3d subshell has 2 unpaired electrons)

4. **Count the Unpaired Electrons**:
- MnSO4 · 4H2O: 5 unpaired electrons
- CuSO4 · 5H2O: 1 unpaired electron
- FeSO4 · 6H2O: 4 unpaired electrons
- NiSO4 · 6H2O: 2 unpaired electrons

5. **Determine the Compound with the Lowest Paramagnetism**:
- The compound with the least number of unpaired electrons is CuSO4 · 5H2O, which has only 1 unpaired electron. Therefore, it exhibits the lowest degree of paramagnetism among the given options.

### Conclusion:
The compound that shows the lowest degree of paramagnetism per mole at 298 K is **CuSO4 · 5H2O**.