More number of oxidation states are exhibited by the actinoids than by the lanthanoids. The main reason for…
More number of oxidation states are exhibited by the actinoids than by the lanthanoids. The main reason for this is:
more active nature of the actinoids
more energy difference between $5 f$ and $6 d$ orbitals than that between $4 f$ and $5 d$ orbitals
lesser energy difference between $5 f$ and $6 d$ orbitals than that between $4 f$ and $5 d$ orbitals
greater metallic character of the lanthanoids than that of the corresponding actinoids
Solution
Actinides exhibit more number of oxidation states than lanthanides because of lesser energy difference between the $5 f$ and $6 d$ orbitals than that between the $4 f$ and $5 d$ orbitals.
Related Theory
Actinides have a very small energy gap between $5 f$ and $6 d$ orbitals, so they can easily form a variety of configurations and hence they are found to be stable in various oxidation states. Lanthanides are comparatively less electropositive than actinides and due to that reason, they are less reactive than actinides.