29. Solving a chemistry problem

34. The determination of chromium in water was carried out by the atomic absorption method according to the additive method. Samples of the analyzed and standard (12.0 μg/ml) solutions of chromium were introduced into volumetric flasks of 50 ml, diluted to the mark with water, acetylene-nitrous oxide was sprayed into the flame, and the optical density was measured at 357.9 nm. The results are shown below:
Volumes of solutions, ml Analyzed 10 10 10 10
Standard 0 10 20 30
A 0.205 0.296 0.383 0.472