The main reason for larger number of oxidation states exhibited by the actinoids than the corresponding lanthanoids, is :-

Options

A. Lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
B. More energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
C. Greater reactive nature of the actinoids than the lanthanoids
D. Larger atomic size of actinoids than the lanthanoids

Answer

To solve the question regarding the larger number of oxidation states exhibited by actinoids compared to lanthanoids, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Oxidation States**:
- Oxidation states refer to the degree of oxidation of an atom in a compound. The ability of an element to exhibit multiple oxidation states is influenced by its electronic configuration and the energy levels of its orbitals.

2. **Identify the Elements**:
- Actinoids are the elements in the 5f block of the periodic table, while lanthanoids are in the 4f block. The actinoids include elements such as Uranium (U), Plutonium (Pu), and others, while lanthanoids include elements like Cerium (Ce), Neodymium (Nd), etc.

3. **Compare Orbital Energy Levels**:
- The key to understanding the difference in oxidation states lies in the energy levels of the 5f and 6d orbitals for actinoids and the 4f and 5d orbitals for lanthanoids.
- For actinoids, the energy difference between the 5f and 6d orbitals is relatively small, which allows for easier excitation of electrons from the 5f to the 6d orbitals.

4. **Reason for More Oxidation States**:
- Because the 5f and 6d orbitals are closer in energy, actinoids can lose different numbers of electrons more easily, leading to a wider range of oxidation states (such as +2, +3, +4, +5, +6, and +7).
- In contrast, the larger energy difference between the 4f and 5d orbitals in lanthanoids restricts their ability to exhibit multiple oxidation states.

5. **Conclusion**:
- Therefore, the main reason for the larger number of oxidation states exhibited by actinoids compared to lanthanoids is the lesser energy difference between the 5f and 6d orbitals.

### Final Answer:
The correct option is **A**: Lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals.

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