139. Solving a chemistry problem

29. Determine the concentration of the solution (in accordance with the task number) in the indicated units according to the data given in Table 3 (solution "a" - standard, solution "b" - investigated).
Problem number 24
Detected ion or substance Fe3
The reaction of the formation of a colored compound with potassium thiocyanate
Concentration:
a) 0.00186M FeCl2 solution
b) Fe in μg / ml
Layer thickness cm 1.0 0.217
Optical density 5.0 0.033