Answer: All actinides.
- A All actinides
- B All lanthanides
- C Mainly uranium
- D Mainly thorium
Correct answer: A. All actinides
Explanation: All actinides (Z=89-103) are radioactive. The lanthanides include only one radioactive element (promethium, Pm).
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.