The actinoids exhibit a greater 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