a) Light
Light (from the Latin lux, lucis) is the part of electromagnetic radiation that can be perceived by the human eye.
In physics, the term light is considered to be part of the field of radiation known as the electromagnetic spectrum, while visible light expression specifically designates radiation in the visible spectrum.
Light, like all electromagnetic radiation, is made up of elementary particles devoid of mass called photons, whose properties according to the wave-particle duality explain the characteristics of their physical behavior.
Light is that part of the electromagnetic spectrum that is perceived by our eyes.
Of the entire spectrum, the portion that humans can see is very small compared to the other spectral regions. This region, called the visible spectrum, comprises wavelengths from 380 nm to 780 nm. The human eye perceives the light of each of these wavelengths as a different color, therefore, in the decomposition of white light in all its wavelengths, by prisms or by the rain in the rainbow, the eye sees all colors.