Question

The chemical formula of sodium chloride is NaCl. The chemical formula of zinc chloride is ZnCl2. Why is it so ?

Answer 1

because the ion of these are zinc Zn2+ Chloride cl- sodium Na+.

Answer 2

here is your answer the valency of sodium chloride that is Na 1+ so it reacts with 1 chlorine to form sodium chloride.
where as zinc has that is zn has 2 + valency so it needs 2 Cl.
hope it helps