5f, 6d and 7s levels having comparable energies.
4f and 5d levels being close in energies.
the radioactive nature of actinoids.
actinoid contraction.
The reason for greater range of oxidation states in actinoids is attributed to 5f, 6d and 7s levels having comparable energies. The oxidation states range from +2 to +7. The most common oxidation state is +3. Hence, option D is correct.