2NaN3=2Na+3N2. If 0.21 moles of NaN3 reacts, what mass of nitrogen would result

Use the mole ratio: 2 moles of NaN3 : 3 moles of N2

you have : 0.21 moles of NaN3 : x moles N2

Cross multiply: you get 0.3 moles for N2

To find the mass = # of moles * molecular mass

0.3 * 28

= 8.4g