A) molar mass H₂ = 2.0 g/mol
m = n * mm
m = 15.0 * 2.0
m = 30.0 g of H₂
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b) molar mass N₂ = 28.0 g/mol
m = n * mm
m = 3.5 * 28.0
m = 98.0 g of N₂
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c) molar mass of NaOH = 40.0 g/mol
m = n * mm
m = 2.69 * 40.0
m = 107.6 g of NaOH
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hope this helps!