Question

The incorrect statement among the following is:

विकल्प

• Actinoids are highly reactive metals, especially when finely divided.

• Actinoid contraction is greater for element to element than lanthanoid contraction.

• Most of the trivalent lanthanoid ions are colourless in the solid state.

• Lanthanoids are good conductors of heat and electricity.

Answer 1

Most of the trivalent lanthanoid ions are colourless in the solid state.

Explanation:

Lanthanoid (Ln³⁺) ions are mostly coloured, not colourless. This is because of the presence of unpaired 4f electrons, which allow f-f electronic transitions. These transitions are weak but still give rise to pale colours. Only ions with no unpaired 4f electrons, like La³⁺ or Lu³⁺, are colourless.