Which of the following compounds is(are) coloured due to charge transfer spectra and not due to d - d transitions?

Options

A. `K_(2)Cr_(2)O_(7)`
B. `KMnO_(4)`
C. `CrO_(3)`
D. All of these

Answer

To determine which of the given compounds are colored due to charge transfer spectra and not due to d-d transitions, we need to analyze the oxidation states of the central metal ions in each compound. The key point is that charge transfer spectra occur when there are no d electrons available for d-d transitions.

### Step-by-Step Solution:

1. **Understanding Charge Transfer Spectra vs. d-d Transitions**:
- d-d transitions occur when there are d electrons present in the metal ion, allowing for electronic transitions within the d orbitals.
- Charge transfer spectra occur when an electron is transferred between the metal and a ligand, which typically happens when the metal is in a high oxidation state and has no d electrons.

2. **Analyzing Each Compound**:
- We will calculate the oxidation states of the central metal ions in the given compounds.

3. **Compound 1: K2Cr2O7 (Potassium Dichromate)**:
- Potassium (K) has an oxidation state of +1.
- Let the oxidation state of chromium (Cr) be \( x \).
- The equation for the compound is:
\[ 2(+1) + 2x + 7(-2) = 0 \]
\[ 2 + 2x - 14 = 0 \implies 2x = 12 \implies x = +6 \]
- Chromium is in the +6 oxidation state, meaning it has no d electrons available for d-d transitions. Therefore, it shows color due to charge transfer spectra.

4. **Compound 2: KMnO4 (Potassium Permanganate)**:
- Potassium (K) has an oxidation state of +1.
- Let the oxidation state of manganese (Mn) be \( x \).
- The equation for the compound is:
\[ +1 + x + 4(-2) = 0 \]
\[ 1 + x - 8 = 0 \implies x = +7 \]
- Manganese is in the +7 oxidation state, which means it also has no d electrons available for d-d transitions. Thus, it shows color due to charge transfer spectra.

5. **Compound 3: CrO3 (Chromium Trioxide)**:
- Let the oxidation state of chromium (Cr) be \( x \).
- The equation for the compound is:
\[ x + 3(-2) = 0 \]
\[ x - 6 = 0 \implies x = +6 \]
- Chromium is again in the +6 oxidation state, indicating no d electrons are present. Therefore, it shows color due to charge transfer spectra.

6. **Conclusion**:
- All three compounds (K2Cr2O7, KMnO4, and CrO3) are colored due to charge transfer spectra and not due to d-d transitions.

### Final Answer:
All of the given compounds (K2Cr2O7, KMnO4, and CrO3) are colored due to charge transfer spectra.

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