Which instrument is designed to separate light into colors and create an image of the resulting spectrum?

The instrument designed to separate light into its constituent colors and create an image of the resulting spectrum is a spectrograph. A spectrograph utilizes a diffraction grating or a prism to disperse light into various wavelengths, which can then be captured and recorded visually or electronically, resulting in a detailed spectrum. This spectrum provides crucial information about the light source, such as its composition, temperature, and movement, making spectrographs invaluable in fields such as astronomy and chemical analysis.

While a prism can also separate light into colors, it does not create a detailed image of the spectrum in the same way that a spectrograph does. A photometer measures the intensity of light without producing an image of its spectrum, and a reflector is primarily used to direct light rather than analyze its spectral composition. Thus, the spectrograph stands out as the correct choice for this function.