I assume that NO2 is being reacted with water
First we need the balanced equation for this reaction: 3 NO2(g) + H2O(l) = 2 HNO3(aq) + NO(g)
Second, find moles of NO2:
(400.g NO2)/(46.01g/mol NO2) = 8.69mol NO2
Third, multiply moles by the mole ratios of NO2 to HNO3 to get moles of HNO3: (8.69mol NO2)(2mol HNO3/3mol NO2) = 5.79mol HNO3
Fourth, multiply moles of HNO3 by its molar mass: (5.79mol HNO3)(63.01g/mol HNO3) = 365g HNO3 produced
