The reason for greater range of oxidation states in actinoids is attributed to:
The radioactive nature of actinoids
5f,6dand7s levels having comparable energies
4fand5d levels being close in energies
The correct option is C5f,6dand7s levels having comparable energies Minimum or comparable energy gap between 5f,6d and7s subshell makes electron excitation easier. Hence, there is a greater range of oxidation states in actinoids.