The colour of potassium dichromate is due to

Options

A. d - d transition
B. transition in `K^+` ion
C. ligand- to - metal charge transfer
D. metal to ligand charge transfer

Answer

To determine the color of potassium dichromate, we can analyze the factors that contribute to its coloration. Here’s a step-by-step solution:

### Step 1: Understanding Potassium Dichromate
Potassium dichromate (K₂Cr₂O₇) contains the dichromate ion (Cr₂O₇²⁻). The chromium in this ion is in the +6 oxidation state.

**Hint:** Remember that the oxidation state of an element can influence its electronic configuration and the resulting color.

### Step 2: Electronic Configuration of Chromium
In the +6 oxidation state, chromium has lost all its 4s and 3d electrons, resulting in an electronic configuration similar to that of argon (Ar). This means that there are no d-electrons in the chromium ion in this state.

**Hint:** The electronic configuration is crucial for understanding how transitions occur in transition metal complexes.

### Step 3: Color Origin in Transition Metal Compounds
The color of transition metal compounds often arises from electronic transitions. These can include:
- d-d transitions (between d-orbitals)
- Ligand to metal charge transfer (LMCT)
- Metal to ligand charge transfer (MLCT)

**Hint:** Different types of transitions absorb different wavelengths of light, which determines the color observed.

### Step 4: Ligand to Metal Charge Transfer
In the case of potassium dichromate, the color is primarily due to ligand to metal charge transfer (LMCT). This occurs when an electron is excited from a ligand orbital to a metal orbital.

**Hint:** LMCT is a significant factor in determining the color of compounds where ligands have strong field effects.

### Step 5: Conclusion
Thus, the color of potassium dichromate is due to the ligand to metal charge transfer, which involves the absorption of specific wavelengths of visible light.

**Final Answer:** The color of potassium dichromate is due to ligand to metal charge transfer.

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