PLEASE HELP (25 POINTS) I've done the rest but these last 3 questions, I need help on :) We are given the answer but need to show the work to getting that answer for credit. Even just instructions will help, thank you!
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1.) Calculate the mass in grams of 3.50 x 10^25 atoms of lithium.
404g Li
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2.) How many molecules of Mg3N2 (magnesium nitride) are formed when excess Mg (magnesium) reacts with 24.3 moles of N2 (nitrogen gas)?
3Mg(s) + N2(g) → Mg3N2(2)
43.1 molecules Mg3N2
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3.) 32.5 grams of NaOH (sodium hydroxide) reacts an excess of CO2 (carbon dioxide).
2NaOH(s) + CO2(g) → Na2CO3(s) + H2O(I)

a.) What is the theoretical yield of Na2CO3 in grams?
43.1g Na2CO3

b.) If 16.45g of Na2CO3 is formed, what is the percent yield?
38.2%
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Will mark brainliest! :)