Answer: Iron (Fe).
- A Iron (Fe)
- B Platinum (Pt)
- C Vanadium (V)
- D Nickel (Ni)
Correct answer: A. Iron (Fe)
Explanation: Iron (with K2O and Al<sub>2</sub>O<sub>3</sub> promoters) is the catalyst in the Haber process for ammonia synthesis.
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.