The correct option is C 18×1023
N2+3H2→2NH3
According to the balanced equation, one mole of N2 reacts with 3 moles of H2
So, 4 moles of N2 will require 12 moles of H2 but only 3 moles of H2 is given. Hence H2 is the limiting reagent.
∴ moles of N2 left =4−1=3
∴ Number of molecules of N2 left =3×6×1023=18×1023