There is no `d-d` transition in `Cu^(+)` but `Cu_(2)O` is coloured due to

Options

A. The presence of unpaired electron
B. The presence of coloured `O^(2-)` ion
C. Charge transfer from oxygen to metal
D. Charge transfer from metal to oxygen

Answer

To solve the question regarding the absence of `d-d` transitions in `Cu^(+)` and the color of `Cu2O`, we can break it down step by step:

### Step 1: Understanding the Electronic Configuration of Copper
- Copper (Cu) has the electronic configuration of `[Ar] 3d10 4s1`. When it loses one electron to form `Cu^(+)`, its configuration becomes `3d10`.

**Hint:** Remember that `d-d` transitions require unpaired electrons in the d-orbitals.

### Step 2: Analyzing `Cu^(+)`
- In the `Cu^(+)` state, all d-orbitals are fully filled (3d10), meaning there are no unpaired electrons. Since `d-d` transitions involve the excitation of electrons from one d-orbital to another, the absence of unpaired electrons means that `Cu^(+)` cannot undergo `d-d` transitions.

**Hint:** Check for unpaired electrons to determine if `d-d` transitions are possible.

### Step 3: Color of `Cu2O`
- `Cu2O` is known to be red in color. The color arises from the electronic transitions that occur within the compound.

**Hint:** The color of a compound often indicates the presence of certain electronic transitions or charge transfers.

### Step 4: Identifying the Cause of Color in `Cu2O`
- The color in `Cu2O` is primarily due to charge transfer processes. In this case, the oxygen ions (O^(2-)) can donate electrons to the copper ions (Cu^(+)). This charge transfer from the oxygen to the metal contributes to the observed color.

**Hint:** Look for electron donation or acceptance processes when analyzing the color of compounds.

### Step 5: Conclusion
- Therefore, the reason `Cu2O` is colored is due to charge transfer from the oxygen ions to the copper ions, not due to `d-d` transitions or unpaired electrons in the copper.

**Final Answer:** The color of `Cu2O` is due to charge transfer from oxygen to metal.