How many nitrogen gas, hydrogen gas, and ammonia molecules would be needed in order for this chemical equation to follow the law of conservation of mass?

N2+H2 > NH3

1 nitrogen gas molecule, 1 hydrogen gas molecule, 1 ammonia molecule
1 nitrogen gas molecule, 1 hydrogen gas molecule, 2 ammonia molecules
1 nitrogen gas molecules, 3 hydrogen gas molecules, 2 ammonia molecules
2 nitrogen gas molecules, 3 hydrogen gas molecules, 2 ammonia molecules