How many moles of Nitrogen in 40.0 g of N2O?
.14 g
25.5 g
14.5 g

To do this question. we first have to find the mass% of nitrogen in N2O and then, using that percentage, we can simply find the number of moles of N from the number of moles of N2O

Mass % of Nitrogen:

Mass% of nitrogen = (Molar mass of N2 / Molar mass of N2O)*100

Mass% nitrogen = (28 / 44)*100

Mass% of Nitrogen = 0.63 * 100

Mass% nitrogen = 63%

Mass of Nitrogen:

So, now we can say that in any given mass of N2O. 63% of the total mass is the mass of Nitrogen

Hence, total mass * 63/100 = Mass of Nitrogen

Replacing the variables

40 * 0.63 = Mass of Nitrogen

Mass of Nitrogen = 25.2 grams