Consider the reaction
N2 + 3H2 ==2NH2:
Calculate the moles of NH3 produced when 0.75 moles of N2 react.
I have corrected the typo.
N2 + 3H2 ==2NH3
Since 1 mol N2 produces 2 mols NH3, then 0.75 mols N2 will produce 2*0.75 = 1.5 mols NH3. Or to do it another way,
0.75 mols N2 x (2 mols NH3/1 mol N2) = 0.75 x 2/1 = 1.5 moles no matter how you do it.