Correct option is C
The red color of rubies is due to the red emission (phosphorescence) of Cr³⁺ ions. The chromium ions (Cr³⁺) embedded in the crystal lattice of ruby are the primary cause of its distinctive red color. When these Cr³⁺ ions absorb light, they undergo transitions that result in the emission of red light, which is characteristic of the ruby. This emission is often classified as phosphorescence because the Cr³⁺ ions can emit light after absorbing energy from the surrounding environment. The absorption of light occurs in the green and blue region of the spectrum, and the red light is reflected, making the ruby appear red.
