Which of the following complex is colourless ?

Options

A. `MnO_(4)^(-)`
B. `[Ni(H_(2)O)_(6)]^(2+)`
C. `[Cu(CH_(3)CN)_(4)]^(+)`
D. `[Cr(H_(2)O)_(6)]^(3+)`

Answer

To determine which of the following complexes is colorless, we need to analyze the electronic configurations of the metal ions involved in the complexes and their d-orbitals.

### Step-by-step Solution:

1. **Understand the Color of Coordination Compounds**:
- Coordination compounds can exhibit color due to the presence of unpaired electrons in their d-orbitals. The color arises from d-d transitions, where an electron jumps from a lower energy d-orbital to a higher energy d-orbital when light is absorbed.

2. **Identify the Electronic Configuration**:
- Complexes with a d^0 (no d-electrons) or d^10 (fully filled d-orbitals) configuration typically do not have unpaired electrons and therefore do not exhibit color. They are usually colorless.

3. **Examine the Given Complexes**:
- If the question provides specific complexes, identify the central metal ion in each complex and determine its oxidation state.
- Use the periodic table to find the electronic configuration of the metal ion in the complex.

4. **Determine the d-Electron Count**:
- For each metal ion, calculate the number of d-electrons based on its oxidation state.
- For example, if the metal is in the +2 oxidation state and normally has 10 d-electrons, it will have 8 d-electrons in the +2 state.

5. **Classify the Complexes**:
- If a complex has a d^0 or d^10 configuration, it will be colorless.
- If it has an incomplete d-orbital (d^1 to d^9), it will likely be colored.

6. **Conclusion**:
- After analyzing all the complexes, identify which one has a d^0 or d^10 configuration and thus is colorless.