Which wave interaction is responsible for the colorful rainbows seen on the backs of CDs?

The colorful rainbows seen on the backs of CDs are primarily due to the phenomenon of diffraction. When light waves hit the closely spaced grooves on the CD's surface, they spread out and interfere with one another, creating a spectrum of colors. This interaction, along with constructive and destructive interference, results in the vibrant rainbow effect. Additionally, the effect is enhanced by the reflection of light from the surface of the CD.