The reactant which is present in the lesser amount, i.e. which limits the amount of product formed is called limiting reagent.When 56 g of N2​+10 g2​ of H2​ is taken as a combination then dihydrogen (H2​) act as a limiting reagent in the reaction.
Here, H2​ gas does not act as limiting reagent .
since 7.5 g2​ of H2​ gas is required for 35 g of N2​ and 8 g of H2​ is present in reaction mixture.
Mass of H2​ left unreacted=8−7.5 gofH2​=0.5 g of H2​
Similarly, in option (c) and (d), H2​ does not act as limiting reagent.
For 14 g of N2​+4 g of H2​.
As we know 28 g of N2​ reacts with 6 g of H2​.
14 g of N2​ reacts with 286​×14 g2​ of H2​⇒3 g of H2​.
For 28 g of N2​+6 g of H2​, i.e. 28 g of N2​ reacts with 6 g of H2​ (by equation I).