The chemical reaction between N2H4 and H2O2 produces nitrogen gas N2 and water H2O. The balanced chemical equation of the reaction is:
N2H4 + 2 H2O2 --> N2 + 4 H2O
One reaction involves one mole of N2H4 reacting with 2 moles of H2O2 to give one mole of N2 and 4 moles of water.
The mass of nitrogen produced is the mass of nitrogen in the N2H4 that is reacting with the H2O2.
21.2 grams of N2H4 takes part in the reaction. The mass of N2 in the 21 g of N2H4 is (28/32)*21.2 = 18.55 g
The mass of nitrogen produced when 21.2 g of N2H4 reacts with 29.2 g of H2O2 producing nitrogen gas and water is 18.55 g.