The chemical formula of ammonia is written as NH3 we can just use the ratio of the atoms since we are not given the reaction. We also make use the avogadro's number to convert from moles to molecules. We calculate as follows:
5.01 x 10^-4 g H2 ( 1 mol / 2.02 g H2 ) ( 2 mol NH3 / 3 mol H2 ) ( 6.022x10
^23 molecules / 1 mol ) = 9.96 x 10^19 molecules NH3
So that he does not get shot and he can take care of the shooter first.