Final answer:
Two atoms of sodium react with one molecule of chlorine gas to produce two units of sodium chloride. With the provided quantities, 10 atoms of sodium will react with 5 molecules of chlorine, leaving 8 atoms of chlorine unreacted.
Step-by-step explanation:
The question involves a chemical reaction between sodium and chlorine to form sodium chloride (NaCl). According to the equation 2 Na (s) + Cl2(g) → 2 NaCl (s), two atoms of sodium react with one molecule of chlorine (which consists of two atoms of chlorine) to produce two formula units of sodium chloride. Therefore, to completely react with 10 atoms of sodium, 5 molecules of chlorine gas would be needed, resulting in 10 atoms of chlorine in the product. If we begin with 16 atoms of chlorine, this would correspond to 8 atoms of chlorine in excess, since two atoms are used for each molecule of Cl2 that reacts. The remaining chlorine atoms would not be part of the sodium chloride and could either remain unreacted or be a part of another reaction if other reactants were present.