The incorrect statement among the following is :
- 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 colorless in the solid state.
- Lanthanoids are good conductors of heat and electricity.
Answer
(3) Most of the trivalent Lanthanoid ions are colorless in the solid state.
Solution
⇒ As per NCERT, the actinoid metals are highly reactive, especially when finely divided — (1) is correct.
⇒ The actinoid contraction is greater from element to element than the lanthanoid contraction, due to poorer shielding by 5f electrons — (2) is correct.
⇒ As per NCERT, many trivalent lanthanoid ions are coloured both in the solid state and in aqueous solution (due to the presence of f electrons); only La3+ and Lu3+ (f0, f14) are colourless — (3) is incorrect.
⇒ Lanthanoids are metals and are good conductors of heat and electricity — (4) is correct.
Answer: (3)