Which one of the following is the medium in optical storage system for reading and recording data?

Optical storage systems, such as Compact Discs (CDs), Digital Versatile Discs (DVDs), and Blu-ray discs, utilize laser light (Light Amplification by Stimulated Emission of Radiation) as the medium to read and record data. These systems work by focusing a laser beam onto the spinning disc's surface, which contains microscopic features called pits and lands.

• Reading: A low-power laser reflects off the disc. A sensor detects changes in the intensity of the reflected light, which the system interprets as binary data (0s and 1s).
• Recording: A higher-intensity laser beam is used to physically or chemically alter the disc's surface (e.g., burning pits into a dye layer) to store information.

Different technologies use different laser wavelengths: CDs use infrared (780 nm), DVDs use red (650 nm), and Blu-ray uses blue-violet (405 nm) lasers.