What is the absorbance maximum for the Evelyn-Malloy method?

• A. 560 nm
• B. 450 nm
• C. 600 nm
• D. 520 nm

Answer: (A)

The key idea here is that the absorbance maximum is the wavelength where the colored product formed in a colorimetric reaction absorbs light most strongly. For the Evelyn-Malloy method, the colored complex produced has its highest molar absorptivity at about 560 nm. Measuring at this wavelength captures the strongest signal, giving the most sensitive and reliable link between concentration and absorbance. Wavelengths away from this peak show less absorption, reducing sensitivity and increasing potential interference, so 560 nm is the optimal choice. The color at this peak sits in the yellow-green region of the visible spectrum, consistent with a strong absorbance there.