Which type of monochromator produces the purest monochromatic light in the UV range?

The correct choice is the option that states a prism and a variable exit slit. A prism separates light into its component wavelengths through refraction, allowing for the selection of very specific wavelengths while minimizing the presence of unwanted wavelengths. This optical property makes prisms particularly effective in producing pure monochromatic light across various ranges, including the ultraviolet region.

Using a variable exit slit enhances the capability to fine-tune the wavelength output. By adjusting the slit width, it is possible to optimize the monochromatic light quality, ensuring minimal stray light and higher purity in the UV range. This combination of a prism’s ability to disperse light accurately and the control of a variable exit slit facilitates the generation of high-purity monochromatic light, which is crucial for precise optical applications in clinical chemistry.

Other methods, such as diffraction gratings, filters, or fixed slits, may have some advantage in certain contexts, but they may introduce additional complexity or less pure light spectra, making them less effective for applications specifically demanding high purity in monochromatic light, particularly in the UV range.