How many moles are present in 10.0 L of nitrogen gas at STP?
Assuming ideal behaviour, 1 mole of any gas occupies 22.4L at STP.
So, moles of 10L = 10/22.4 moles
= 0.4464 moles
do you mean the percentage by mass of nitrogen or oxygen in nitrogen oxide? First work out the mass of one mole of nitrogen oxide Then work out the mass of the number of moles of nitrogen / oxygen in one mole of nitrogen oxide Divide this by the mass of one mole of nitrogen oxide and then multiply by 100.