There is a greater range of oxidation state among the actionids than that in the lanthanoids. Why ?

Explanation

Actinoids form compounds with large number of oxidation state as there is very little energy difference between 5f, 6d and 7s orbital. So electron can be ejected from all the three orbitals leading to the formation of various oxidation states. Compare to actinoids, 4f-orbital is relatively lower in energy withrespect to 5d & 6s-orbitals. This gives limited access to the 4f-electron during bond formation. Thus they show only limited number of oxidation states in their compounds.