144. Solving a chemistry problem

80. (1) A portion of silicate weighing 0.2000 g was dissolved in a mixture of H2SO4 and HF, the solution was evaporated, the residue was treated with hydrochloric acid and transferred to a volumetric flask with a capacity of 200.00 ml. Determination of sodium in the sample was performed by the method of calibration curve. Before measuring the analyzed solution was diluted 2 times. Received the following data for the construction of the calibration curve:
C (Na) mg / l 2.5 5.0 7.5 10.0
I mA 10 20 30 40
Determine the mass fraction of sodium in silicates for the following options.
Option 1
I (Na) = 1.00 mA