A sample of blue copper (II) sulfate is analyzed using a spectrophotometer (or colorimeter). When analyzed by four different wavelengths, the solution obtain the following absorbance data:
∙425 nm=0.12
∙480 nm=0.25
∙510 nm=0.98
∙610 nm=0.11
What is the optimum wavelength(s) to be used for analysis?