Which one of the following ions exhibits d-d transition and paramagnetism as well ?

Options

A. `MnO_(4)^(-)`
B. `Cr_(2)O_(7)^(2-)`
C. `CrO_(4)^(2-)`
D. `MnO_(4)^(2-)`

Explanation

To solve the question "Which one of the following ions exhibits d-d transition and paramagnetism as well?", we need to analyze the electronic configurations and oxidation states of the given ions.

### Step-by-Step Solution:

1. **Understanding d-d Transition and Paramagnetism**:
- **d-d Transition**: This occurs when an electron in a d-orbital absorbs energy and jumps to a higher energy d-orbital. This is only possible if there are unpaired electrons present in the d-orbitals.
- **Paramagnetism**: This property is exhibited by species that have unpaired electrons. The presence of unpaired electrons makes the species attracted to a magnetic field.

2. **Analyzing Each Ion**:
- **Option 1: MnO4⁻**:
- Manganese (Mn) is in the +7 oxidation state.
- Electronic configuration: Argon (Ar) 3d⁰.
- Unpaired electrons: 0 (Diamagnetic).
- Conclusion: No d-d transition and not paramagnetic.

- **Option 2: Cr2O7²⁻**:
- Chromium (Cr) is in the +6 oxidation state.
- Electronic configuration: Argon (Ar) 3d⁰.
- Unpaired electrons: 0 (Diamagnetic).
- Conclusion: No d-d transition and not paramagnetic.

- **Option 3: CrO4²⁻**:
- Chromium (Cr) is also in the +6 oxidation state.
- Electronic configuration: Argon (Ar) 3d⁰.
- Unpaired electrons: 0 (Diamagnetic).
- Conclusion: No d-d transition and not paramagnetic.

- **Option 4: MnO4²⁻**:
- Manganese (Mn) is in the +6 oxidation state.
- Electronic configuration: Argon (Ar) 3d⁵.
- Unpaired electrons: 5 (Paramagnetic).
- Conclusion: Yes, d-d transition is possible due to unpaired electrons.

3. **Final Answer**:
- The ion that exhibits both d-d transition and paramagnetism is **MnO4²⁻**.