Which of the statements below are correct?

A. Actinoid contraction is greater than lanthanoid contraction.

B. The magnetic property of the actinoids are more complex than those of the lanthanoids.

C. Actinoid contraction taking place due to poor shielding by 5f electrons.

D. Actinoid contraction taking place due to poor shielding by 6f electrons.

Choose the correct answer from the options given below:

A, B and C only

The correct answer is option 2. A, B and C only.

Lets delve into each statement regarding actinoid and lanthanoid series:

Statement A: Actinoid contraction is greater than lanthanoid contraction.

Lanthanoid Contraction: This refers to the gradual decrease in the size of lanthanide ions (from La³⁺ to Lu³⁺) despite the addition of more electrons. This contraction is due to the poor shielding of the nuclear charge by the 4f electrons, which leads to a greater effective nuclear charge experienced by the outer electrons.

Actinoid Contraction: Similar to the lanthanoids, the actinoids (from Ac³⁺ to Lr³⁺) also show a decrease in ionic radius as more electrons are added. However, the actinoid contraction is more pronounced. This is because 5f electrons in actinoids are less effective at shielding the nuclear charge compared to 4f electrons in lanthanides, leading to a greater effective nuclear charge and thus, a greater contraction.

Statement B: The magnetic property of the actinoids are more complex than those of the lanthanoids.

Magnetic Properties: The magnetic behavior of elements is influenced by the unpaired electrons and their arrangement in the atomic orbitals. In lanthanides, the 4f electrons are relatively localized and contribute to magnetic properties in a more predictable manner.

Actinoids: In contrast, the 5f electrons in actinoids have more complex interactions due to their greater spatial extent and involvement in various bonding and electronic states. This leads to more varied and complex magnetic behaviors, including a wider range of magnetic susceptibilities and interactions.

Statement C: Actinoid contraction taking place due to poor shielding by 5f electrons.

Shielding Effect: The 5f electrons in the actinoid series are less effective at shielding the nuclear charge compared to the 4f electrons in the lanthanide series. This poor shielding leads to a stronger attraction between the nucleus and the outer electrons, causing a more significant contraction in the size of the actinoid ions.

Contraction: As the number of protons increases with each successive element in the actinoid series, the poor shielding effect means that the electrons are pulled closer to the nucleus, causing a greater contraction in the ionic and atomic sizes.

Statement D: Actinoid contraction taking place due to poor shielding by 6f electrons.

Incorrect Attribution: This statement is incorrect because there are no 6f electrons involved in the actinoid series. The actinoids involve the 5f electrons, not 6f. The actinoid contraction is due to the poor shielding by the 5f electrons, not by 6f electrons. There is no 6f orbital in the actinoid series to contribute to shielding.

To sum up:

Statement A is correct because actinoid contraction is indeed greater than lanthanoid contraction due to poorer shielding by the 5f electrons.

Statement B is correct because the magnetic properties of actinoids are more complex due to the involvement of 5f electrons.

Statement C is correct because actinoid contraction is due to poor shielding by 5f electrons.

Statement D is incorrect because actinoid contraction is not related to 6f electrons, as there are no such orbitals in the actinoid series.

Thus, the correct statements are: 2. A, B and C only