Explain how many grams of solid magnesium nitrate should be added to 5.0 g of solid sodium nitrate in a 500-mL volumetric flask in order to produce an aqueous 0.25 M solution of NO3- ions once the flask is filled to the 500.-mL volume line?
A. 28 g
B. 9.8 g
C. 2.5 g
D. 4.9 g
E. 14 g