Which of the following complexes will show maximum paramagnetism ?

Options

A. `3d^(4)`
B. `3d^(5)`
C. `3d^(6)`
D. `3d^(7)`

Explanation

To determine which of the given complexes will show maximum paramagnetism, we need to analyze the number of unpaired electrons in each of the d-electron configurations provided: 3d4, 3d5, 3d6, and 3d7. Paramagnetism is directly related to the presence of unpaired electrons; the more unpaired electrons a complex has, the more paramagnetic it is.

### Step-by-Step Solution:

1. **Identify the d-electron configuration:**
- We have four configurations to analyze: 3d4, 3d5, 3d6, and 3d7.

2. **Determine the number of unpaired electrons for each configuration:**
- **For 3d4:**
- The electron configuration can be represented as: ↑↓ ↑ ↑ ↑
- Number of unpaired electrons = 4 (since there are 4 electrons occupying separate orbitals).

- **For 3d5:**
- The electron configuration can be represented as: ↑↓ ↑ ↑ ↑ ↑
- Number of unpaired electrons = 5 (all five electrons occupy separate orbitals).

- **For 3d6:**
- The electron configuration can be represented as: ↑↓ ↑ ↑ ↑ ↑ ↑
- Number of unpaired electrons = 4 (the first five electrons occupy separate orbitals, and the sixth pairs with one of them).

- **For 3d7:**
- The electron configuration can be represented as: ↑↓ ↑ ↑ ↑ ↑ ↑ ↑
- Number of unpaired electrons = 3 (the first five electrons occupy separate orbitals, and two of the next electrons pair up).

3. **Compare the number of unpaired electrons:**
- 3d4 has 4 unpaired electrons.
- 3d5 has 5 unpaired electrons.
- 3d6 has 4 unpaired electrons.
- 3d7 has 3 unpaired electrons.

4. **Conclusion:**
- The complex with the maximum number of unpaired electrons is 3d5, which has 5 unpaired electrons. Therefore, it will show the maximum paramagnetism.

### Final Answer:
The complex that will show maximum paramagnetism is **3d5**.