Which of the following statements is not true for `Ce^(3+)` and `Yb^(3+)`?

Options

A. Both absorb in UV region
B. Both show f-f transition
C. Both show 4f to 5d transition
D. Both ions are colorless

Answer

To determine which statement is not true for \( \text{Ce}^{3+} \) and \( \text{Yb}^{3+} \), we will analyze the properties of these ions step by step.

### Step 1: Identify the Elements
Both \( \text{Ce}^{3+} \) (Cerium) and \( \text{Yb}^{3+} \) (Ytterbium) are f-block elements and belong to the lanthanide series.

### Step 2: Color Properties
Both \( \text{Ce}^{3+} \) and \( \text{Yb}^{3+} \) are colorless in their ionic forms. This means they do not absorb visible light.

### Step 3: Absorption in UV Region
Although they are colorless and do not absorb in the visible region, both ions show strong absorption in the ultraviolet (UV) region. This absorption is due to electronic transitions.

### Step 4: Type of Electronic Transition
The electronic transitions that occur in \( \text{Ce}^{3+} \) and \( \text{Yb}^{3+} \) are from the \( 4f \) orbitals to the \( 5d \) orbitals (often referred to as \( 4f \rightarrow 5d \) transitions). This is not an \( f \rightarrow f \) transition.

### Step 5: Analyze the Statements
Now we will evaluate the statements given in the question:

1. **Both absorb in UV region** - This statement is true.
2. **Both show f-f transition** - This statement is not true, as the transitions are \( 4f \rightarrow 5d \), not \( f \rightarrow f \).
3. **Both show \( 4f \rightarrow 5d \) transition** - This statement is true.
4. **Both ions are colorless** - This statement is true.

### Conclusion
The statement that is not true for \( \text{Ce}^{3+} \) and \( \text{Yb}^{3+} \) is the second one: "Both show f-f transition."

Thus, the correct answer is **option B**.

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