Question

The incorrect statement among the following is :

• A. Actinoid contraction is greater for element to element than Lanthanoid contraction.
• B. Most of the trivalent Lanthanoid ions are colorless in the solid state.
• C. Lanthanoids are good conductors of heat and electricity.
• D. Actinoids are highly reactive metals, especially when finely divided

Answer 1

The Correct Option is B

To determine the incorrect statement among the given options, let's analyze each statement based on our knowledge of chemistry, focusing on the properties of Lanthanoids and Actinoids.

1. Actinoid contraction is greater for element to element than Lanthanoid contraction.
   • Both Lanthanoids and Actinoids experience a contraction in their atomic and ionic sizes across the series due to the filling of 4f and 5f orbitals, respectively.
   • However, Actinoid contraction is more pronounced than Lanthanoid contraction because 5f orbitals, involved in Actinoids, are less shielded and have poor shielding effect compared to 4f orbitals in Lanthanoids.
   • Therefore, this statement is correct.
2. Most of the trivalent Lanthanoid ions are colorless in the solid state.
   • Trivalent Lanthanoid ions (Ln³⁺) typically show colors in the solid state due to f-f transitions. These transitions involve the partially filled 4f orbitals, which cause absorption of specific wavelengths of light, giving rise to their characteristic colors.
   • Most Lanthanoid ions are colored rather than colorless except for the few like La³⁺ and Lu³⁺ which have empty or completely filled 4f subshells. Hence, this statement is incorrect.
3. Lanthanoids are good conductors of heat and electricity.
   • Lanthanoids are metals and exhibit good conductivity for heat and electricity, similar to other metals.
   • Thus, this statement is correct.
4. Actinoids are highly reactive metals, especially when finely divided.
   • Actinoids are indeed highly reactive, particularly in their finely divided state. This high reactivity is due to the presence of partially filled 5f orbitals.
   • Therefore, this statement is correct.

Based on the analysis above, the statement that is incorrect is: Most of the trivalent Lanthanoid ions are colorless in the solid state.