Question

Why is only one molecule of N2 needed to produce 2 molecules of NH3?

Answer 1

Because in one molecule of N2, there are 2 atoms of N.

Answer 2

And in 2 molecules of NH3, there are also 2 atoms of N.

Answer 3

So, 1 molecule of N2 and 3 molecules of H2 make 2 molecules of NH3

Answer 4

N2 + 3H2 --> 2NH3
The NH3 only needs one N but N2 is made up of two Ns because it's a diatomic gas so N2 can produce 2NH3
N would make one NH3 but N doesn't come only by itself since its a diatomic gas