Ammonia and oxygen react to form nitrogen and water, like this: 4NH₃(g) + 3O2(g) → 2N2(g) + 6H₂O(g). Imagine 64 mmol of NH₃ and ___ of O2 are added to an empty flask, and then answer:
1) 32 mmol
2) 48 mmol
3) 64 mmol
4) 96 mmol