In the synthesis reaction where two atoms of sodium (Na) combine with one molecule of chlorine gas (Cl2), the balanced equation is:
\[ 2 \text{Na} + \text{Cl}_2 \rightarrow 2 \text{NaCl} \]
From the balanced equation, it is clear that 2 atoms of sodium react with 1 molecule of chlorine gas to produce 2 molecules of sodium chloride.
Therefore, 2 molecules of sodium chloride (NaCl) are produced in this reaction.