for question one please use sig figs! i am so confused

1. Evaluate the following: 0,735 . 0.735 mL + 1.10 mL 1.10 1,835 - 1.84 mL 200 ul-20.0 ML 200 20.0 1804L . (1.3211 g)/(0.9779 mL) 180.0 1,3211 & o. 9779 1,3511m' 10.2 mL +5.10 x 10'L-875 ul (respond in mL) 8.0 mg - 3.11 x 10-6 kg +4598 ug (respond in mg) (3.761 x 103 mol)/(0.431 L) mol . (5.4381 x 10-4 6.20 x 10-2 ML 2)601) (7.551 mL) ) g 2. You have a 9.1 ppm sodium ion (Na+, 22.990 g/mol) aqueous solution. Express this in uM (umol/L). 3. Convert an aqueous sodium ion concentration of 2.87 x 10 mM (Na solution) into ppb. 4. If you weigh out 0.919 g of Copper (II) sulfate pentahydrate (CuSO4-5H20, M = 249.68 g/mol, a translucent blue crystalline solid) and dissolve this in pure water to give a total solution volume of 25.00 ml, what is the molar concentration of the copper sulfate solution you just prepared? 5. Pure caffeine (CsH30NO, M = 194.19 g/mol) is an opaque white crystalline solid. Calculate the grams of caffeine needed to prepare 50.00 mL of a 0.05000 M solution of caffeine. 6. You wish to prepare 100.0 mL of a 1.00 x 102 M solution of sodium (Na, 22.990 g/mol) from pure, solid sodium sulfate (Na2SO4, M = 142.04 g/mol). How many grams of Na2SO4 will you need