The actinoids exhibit more number of oxidation states in general than the lanthanoids. This is because

(a) the 5f orbitals extend further from the nucleus than the 4f orbitals

(b) the 5f orbitals are more buried than the 4f orbitals

(c) there is a similarity between 4f and 5f orbitals in their angular part of the wave function

(d) the actinoids are more reactive than the lanthanoids.