The reason for the greater range of oxidation states in actinoids is attributed to:
the radioactive nature of actinoids
actinoid contraction
5f, 6d and 7s levels having comparable energies
4f and 5d levels being close in energies
The reason for the greater range of oxidation states in actinoids is attributed to 5f, 6d and 7s levels having comparable energies. Due to this outermost electrons are excited to higher energy levels giving variable oxidation states.
Hence, option number (3) is correct.