Answer: Increasing field strength: I- 2 O 3 < en < CN-.
- A Increasing field strength: I- < Br- < Cl- < F- < OH- < H<sub>2</sub>O < NH<sub>3</sub> < en < CN-
- B Decreasing atomic mass of the donor atom across the ligand series under most conditions encountered
- C Charge on the ligand alone, independent of donor atom identity as frequently observed in practice
- D Physical size of the ligand alone, independent of field strength in many documented cases
Correct answer: A. Increasing field strength: I- < Br- < Cl- < F- < OH- < H<sub>2</sub>O < NH<sub>3</sub> < en < CN-
Explanation: The spectrochemical series ranks ligands from weak field (causing small Delta, spin-free) to strong field (large Delta, spin-paired) based on their crystal field splitting ability.
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.