A chemical equation lets us observe the ideal molar ratio between two chemical species that are taking part in a chemical reaction. This ratio is equivalent to the ratio of the stoichometric coefficients of the species. Therefore, the ratio between nitrogen dioxide and nitrogen monoxide is:
3 : 1
If 0.83 moles of nitrogen dioxide are present, the moles of nitrogen monoxide will be:
0.83/3
Moles of nitrogen monoxide are 0.277.