Question

Knowing that the chemistry of lanthanoids (Ln) is dominated by its +3 oxidation state, which of the following statements is incorrect?

• A. The ionic size of \( \text{Ln}^{3+} \) decreases in general with increasing atomic number
• B. \( \text{Ln} (III) \) compounds are generally colourless.
• C. \( \text{Ln} (III) \) hydroxides are mainly basic in character.
• D. Because of the large size of the \( \text{Ln} (III) \) ions, the bonding in its compounds is predominantly ionic in character.

Hint:

Lanthanoid ions in their +3 oxidation state typically form colorless compounds, as they do not undergo electronic transitions that absorb visible light.

Answer 1

The Correct Option is B

Step 1: Analyze the lanthanoid chemistry.
Lanthanoid ions in the +3 oxidation state often form colorless compounds because the d-orbitals are fully occupied and do not absorb visible light.
Step 2: Conclusion.
Thus, the statement that \( \text{Ln} (III) \) compounds are generally colorless is incorrect.
Final Answer: \[ \boxed{\text{Ln (III) compounds are generally colourless.}} \]