Question

2Na + Cl2 - ?NaCI
In the reaction, sodium and chlorine combine to produce sodium chloride. In an instance when eight sodium chloride molecules
are produced, how many diatomic chlorine molecules went into the reaction?

Answer 1

you have 2 Na on the left, so you need 2 Na on the right.
2Na + Cl2 = 2NaCl
Now check the Cl atoms. OK as is: 2 on both sides.
The equation tells you you need 1/2 as many Cl2 as you have NaCl.
So, 4 Cl2 to produce 8 NaCl.