After plotting Absorbance (A) vs. Concentration (M) data for standard solutions

Question

After plotting Absorbance (A) vs. Concentration (M) data for standard solutions of their Fe-bipy complex, some students obtained a plot with an best-fit line equation of: Abs = 8,520[Fe2+-bipy] + 0.002.

               An "unknown" sample was then measured to have an Absorbance of 0.329. If this was for an "unknown" sample that started out as a 100.0 mL Fe3+ solution, and then was diluted to a 2.00mL-in-50.00mL solution, and then finally was diluted in a test tube to 4.00mL-in-10.00mL, what was the concentration of the original 100.0 mL Fe3+ "unknown" solution?

3.5 × 10-5 M

2.4 × 10-3 M

9.6 × 10-4 M

9.6 × 10-5 M

3.5 × 10-5 M

2.4 × 10-3 M

9.6 × 10-4 M

9.6 × 10-5 M

Explanation / Answer

if the absorbance is A = 0.329 then [Fe(3+)] = 0.04 M in the test tube. As you dilute 4ml in 10 ml the C2 = 0.0959M. And then that C2 was diluted 2ml to 50ml C3 = 6.14e-4 M. I know this is not in the answer table but I have already done the calculations too many times and I get the same answer

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