After the reaction represented by 2H2(g)+O2(g)→2H2O(g) goes to completion, which of the following particulate-level descriptions best represents the contents of a closed container that initially held exactly 4 H2 molecules and 2 O2 molecules?
a) 2 H2O molecules only
b) 4 H2O molecules and 2 H2 molecules
c) 4 H2O molecules only
d) 2 H2O molecules and 2 H2 molecules