$HCl$ was passed through a solution of $CaC{l}_2$, $MgC{l}_2$ and $NaCl$. Which of the following compound(s) crystallise(s)?

In a solution of $NaCl$, $CaC{l}_2$, and $MgC{l}_2$, passing $HCl$ gas increases the concentration of $C{l}^{-}$ ions (common ion effect). Since $NaCl$ has a lower solubility compared to the chlorides of $Mg$ and $Ca$, only $NaCl$ precipitates/crystallises out.