Each colour within the visible light spectrum has its own narrow band of __________ and frequency. What one word completes the sentence?

The one word that completes the sentence is "wavelength."

In the context of the visible light spectrum, each color corresponds to a specific range of wavelengths and frequencies. For example, red light has longer wavelengths (approximately 620 to 750 nanometers) and lower frequencies, while violet light has shorter wavelengths (approximately 380 to 450 nanometers) and higher frequencies. This distinction in wavelengths and frequencies is fundamental to understanding the properties of light and how different colors are perceived by the human eye. The visible spectrum is just a small part of the electromagnetic spectrum, which includes other forms of radiation such as infrared and ultraviolet light.