Chemistry - Coordination Chemistry Question with Solution | TestHub
The red colour of ruby is due to
Options:
Answer:
Solution:
Explain the question: Identify the cause of the red color in ruby.
Concept: d-d transitions in transition metal impurities.
Solution:
Composition: Ruby is primarily composed of corundum, which is anhydrous aluminum oxide (Al₂O₃).
Impurity: Its characteristic red color is not from the Al₂O₃ itself, but from trace amounts (about 0.5-1%) of chromium ions (Cr³⁺) that substitute for some Al³⁺ ions in the crystal lattice.
Optical Process: The Cr³⁺ ions (d³ configuration) are surrounded octahedrally by oxide ions. When white light hits the crystal, these ions absorb green and yellow light to promote an electron from a lower energy d-orbital to a higher energy one—a process known as a d-d transition.
Color Observation: The remaining light that is transmitted or reflected is primarily in the red region of the spectrum, giving the gemstone its deep red appearance.
Final Answer: The correct option is (b).