N2 and H2 are mixed in 14:3 mass ratio. After certain time ammonia was found to be 40% by mol. The mole fraction of N2 at that time in mixture of N2 H2 and NH3 is

Thus N2 and H2 Mole ratio 1:1.5 H2 is limiting reagents. At time when 0.4 mole of nh3 is formed when 0.4 mole n2 and 3×.4 mole of h2 .the remaining n2 is .6 &h2 is 0.3 mole present in mixture. Mole fraction of n2=0.6/(.6+.4+.3)=0.4615