How many atoms are there before and after the chemical reaction N2 + 2O2 --> 2NO2

Answer 1

Before reaction:

1 molecule of N₂ (2 nitrogen atoms)

2 molecules of O₂ (4 oxygen atoms)

no molecules of NO₂

After reaction assuming it goes to completion and is not reversible which is a false assumption:

no molecules of N₂

no molecules of O₂

2 molecules of NO₂ (2 atoms of nitrogen and 4 atoms of oxygen)