A larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids, the main reason being:

1. A
   $4f$ orbitals are more diffused than the $5f$ orbitals
2. B
   lesser energy difference between $5f$ and $6d$ than between $4f$ and $5d$ orbitals
3. C
   more energy difference between $5f$ and $6d$ than between $4f$ and $5d$ orbitals
4. D
   more reactive nature of the actinoids than the lanthanoids