A 20-ppm solution of a DNA molecule (unknown moecular weight) isolated from Escherichia coli was found to give an absorbance of 0

Please see the attached file.

1. According to Beer- Lambert law, the absorbance A is

L is the path length, c is the concentration of the chemical.
So the absorptivity
In this problem, we have A=0.8, the path length l = 2 cm.
The concentration of the DNA molecule is
So the absoptivity is

2.
For the c= M solution, it absorbs 31.5% of the radiation at 415 nm.
Let us assume the radiation intensity as I0, then the solution absorbs 31.5%I0 = 0.3I0. So the transmitted intensity is
Then according to Beer - Lambert law,
(1)
(2)
Compare (1) and (2)
(3)
Plug (3) back into (1), the absorbance (4)
The absorptivity and the path length are fixed since it is the same chemical and experiment.

When , the absorbance
The transmittance T is defined as the passed radiation divided by the incident radiation.
So

Now the transmittance is 03244, so the transmitted radiation , then the absorbed radiation is
Therefore, the percent of absorption is 67.56%.

The absorbance is 0.4929, the transmittance is 0.3244.