Answer: 5f orbitals (from Ac, Z=89 to Lr, Z=103).
- A 5f orbitals (from Ac, Z=89 to Lr, Z=103)
- B 4f orbitals, the same set filled by the lanthanide series
- C 6d orbitals, filled instead in the subsequent transactinide series
- D 7s orbitals, which are already filled before the actinides begin
Correct answer: A. 5f orbitals (from Ac, Z=89 to Lr, Z=103)
Explanation: Actinides (Z=89-103) progressively fill 5f orbitals, analogous to lanthanides filling 4f.
Aqueous solutions of transition metal ions show characteristic colours caused by electrons absorbing visible light to jump between split d-orbitals; the exact colour depends on the metal, its oxidation state, and surrounding ligands.
Concept context
Transition metals (d-block) and lanthanides/actinides (f-block). Known for coloured compounds, variable oxidation states, complex formation, and catalytic properties. Frequently tested in JEE and NEET.