Which device selects and transmits a narrow spectral band before detection?

• A. Monochromator
• B. Light
• C. Nebulizer
• D. Flame

Answer: (A)

Isolating a single wavelength before detection is essential in many spectroscopic measurements to improve selectivity and reduce interference. A monochromator does this by dispersing the light into its component wavelengths and using a narrow entrance/exit slit to pass only a small band of wavelengths to the detector. The dispersive element—either a diffraction grating or a prism—separates colors by wavelength, and adjusting the slit width sets how narrow the transmitted band is. Narrowing the band improves spectral resolution and reduces overlap from neighboring wavelengths, though it also reduces signal intensity.

Nebulizers convert liquid samples into an aerosol for introduction to the measurement region; flames primarily act as a source or atomizer and do not filter light by wavelength. A general term like light isn’t a device that selects a spectral band. Therefore, the instrument that best fits “selects and transmits a narrow spectral band before detection” is the monochromator.