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

1. The ionic size of Ln (III) decreases in general with increasing atomic number
2. Ln (III) compounds are generally colourless.
3. Ln (III) hydroxides are mainly basic in character
4. Because of the large size of the Ln (III) ions the bonding in its compounds is predominantly ionic in character.

Correct answer: Ln (III) compounds are generally colourless.

Solution

Ln (III) compounds often exhibit vibrant colors due to f-f electronic transitions, contrary to the statement that they are generally colorless. This characteristic is a result of the partially filled 4f orbitals, which can absorb visible light.

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