Question

Larger number of oxidation states are exhibited by the actinoids than those of lanthanoids. The reason is:

• A. Lesser energy difference between 5f and 6d than between 4f and 5d orbitals
• B. More energy difference between 5f and 6d than between 4f and 5d orbitals
• C. 4f orbitals are more diffused than 5f orbitals
• D. Highly reactive nature of the actinoids

Hint:

The larger number of oxidation states in actinoids is due to the relatively smaller energy difference between the 5f and 6d orbitals, allowing for more flexibility in electron configuration.

Answer 1

The Correct Option is A

Step 1: Consider the electronic configurations of lanthanoids and actinoids.
Lanthanoids and actinoids both belong to the f-block elements, where the f-orbitals play a crucial role in determining the oxidation states. The lanthanoids have their electrons filling the 4f orbitals, while the actinoids have their electrons filling the 5f orbitals.

Step 2: Compare the energy levels of f and d orbitals.
- In the actinoids, the 5f orbitals are closer in energy to the 6d orbitals. This allows actinoids to easily exhibit a greater variety of oxidation states because electrons from both the f and d orbitals can be involved in bonding.
- In contrast, the 4f orbitals in lanthanoids are more tightly bound and more separated from the 5d orbitals, limiting the number of oxidation states they can exhibit.

Step 3: Conclusion.
Thus, the smaller energy difference between the 5f and 6d orbitals in the actinoids allows them to exhibit a larger number of oxidation states compared to the lanthanoids. This makes option (A) the correct answer.