Correct Answer - C
The reason for greater range of oxidation states in actinoid is attributed to the 5f, 6d, and 7s levels having comparable energies.
The 5f-orbitals extend into space beyond the 7s and 6p-orbitals and participate in bonding. This is in direct contrast to the lanthanides where the 4f-orbitals are buried deep inside the atom, totally shielded by outer orbitals and thus unable to take part to bonding.
