Beer's law states that absorbance is related to which factors?

• A. Absorbance is proportional to concentration, path length, and molar absorptivity
• B. Absorbance is proportional to transmittance
• C. Absorbance equals log10(T) where T is transmittance
• D. Absorbance is independent of wavelength

Answer: (A)

Beer's law links how much light a solution absorbs to how concentrated the absorbing species is, how long the light travels through the sample, and how strongly that species absorbs at a given wavelength. The standard expression A = εbc captures this: absorbance increases with concentration (c), with path length (b), and with molar absorptivity (ε), which depends on the wavelength. This is why the statement that absorbance is proportional to concentration, path length, and molar absorptivity is the correct one.

Transmittance, the fraction of light that passes through, is related to absorbance by A = −log10(T), not directly proportional. That makes the option linking absorbance to transmittance incorrect. Absorbance also depends on wavelength because ε changes with wavelength, so it is not independent of wavelength. The idea that absorbance equals log10(T) (instead of the negative log) and that it’s independent of wavelength don’t fit Beer's law.