If a 0.10 m solution of a colored substance has a maximum absorbance at 500 nm and an absorbance of 0.26 m at this wavelength, what will be the measured absorbance of a 0.20 m solution at 500 nm?

Absorbance is related to the concentration of a substance using the Beer-Lambert's Law. According to this law, absorbance is linearly related to concentration. However, this is only true up to a certain concentration depending on the substance. For this case, we assume that the said law is applicable.

A = kC
Using the first conditions, ewe solve for k.
0.26 = k (0.10)
k = 2.6

A = kC
A = 2.6 (0.20) = 0.52

Therefore, the absorbance at a concentration of 0.20 M and wavelength of 500nm is 0.52.