The greatest range of oxidation states in actinoids is partly attributed to the fact that the following set of levels have comparable energies.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 5f, 6d, 7s
The actinoids (Z = 90–103) fill the 5f orbitals; their outer configuration is [Rn] 5f1–14 6d0–1 7s2. The 5f, 6d and 7s levels have comparable energies, so electrons from all three can take part in bonding. This is why the actinoids show a greater range of oxidation states than the lanthanoids (for example +3 to +7 in Np and Pu).
NCERT (2026-27 edition):
Oxidation States – …
