What monochromator specification is needed to measure the true absorbance of a compound having a natural absorption bandwidth of 30 nm?

To measure the true absorbance of a compound effectively, it is essential for the monochromator used in the spectrophotometric measurement to have a bandpass that is narrower than the natural absorption bandwidth of the compound. The rationale behind this is that a narrower bandpass allows for a more precise measurement of the absorbance at the specific wavelength of the compound's peak absorption while minimizing the influence of neighboring wavelengths that could contribute to inaccuracies.

In this case, the compound has a natural absorption bandwidth of 30 nm. A 5-nm bandpass is significantly narrower than this bandwidth, allowing the monochromator to isolate the specific wavelengths where the absorption occurs effectively and to provide a measurement that reflects the true absorbance characteristics of the compound. This tight bandpass will also help reduce any interference from other absorbing species or light scattering, ensuring that the measurement is as accurate as possible.

The other options, which possess wider bandpasses, would average out the absorbance over a larger range of wavelengths. This averaging effect can lead to inaccuracies and misrepresentations of the compound's true absorbance profile. Therefore, utilizing a 5-nm bandpass is the ideal choice for achieving precise and accurate absorbance readings for a compound with a broader absorption range.