Answer: Orange.
- A Orange
- B Purple
- C Blue
- D Green
Correct answer: A. Orange
Explanation: K2Cr2O7 is orange due to the Cr2O72- ion; in alkaline conditions it converts to yellow CrO42-.
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.