140. Solving a chemistry problem

24, 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 Mg2 +
Colored compound formation reaction
Concentration:
a) 0.1 g of MgCl2 in 250 ml of solution
b) Mg (in%) in the mineral when weighed 0.2 g in 50 ml of solution
Layer thickness cm 2.0 3.0
Optical density 0.222 0.046