Correct Answer: Gas plasma

Solution : The correct answer is Gas plasma.

A fluorescent screen is used to view images on the cathode ray tube (CRT), a vacuum tube with an electron gun (also known as an electron emitter or source). Three distinct phosphors are used in colour tubes, and they emit red, green, and blue light, respectively. They are arranged in groups known as "triads" or stripes, similar to aperture grille designs (as in shadow mask CRTs).