126. Solving a chemistry problem

60th century In the photometric determination of a substance by the method of one standard, a sample of a standard substance with a mass m was dissolved in a volumetric flask with a volume of Vk(A), diluted with water to the mark and standard solution A was obtained. An aliquot of solution A with a volume of Va(A) was taken into a volumetric flask with a volume of Vk(B). ), carried out a photometric reaction by adding the necessary reagents to the flask, the volume of the solution was brought up to the mark with water and a reference solution (solution B) was obtained. The optical density of the reference solution was measured in a cuvette with an absorbing layer thickness I at a wavelength λmax corresponding to the maximum light absorption of the photometric reaction product.
Using the data below, calculate what mass m of a sample of the standard substance should be taken so that the optical density of the reference solution is equal to the optimal value at which the relative systematic error of the photometric determination is minimal.
Option B
Determined substance Fe2
Standard substance FeSO4*7H20
Reagent 1,10-phenanthroline (pH 2-9)
λmax 508
εmax 1.11*104
l, cm 1.00
Vk(A), 200
Va(A), 1.00
Vk(B), 50