Solution:
On passing \(\mathrm{HCl}\) through aqueous solution of \(\mathrm{CaCl}_{2}, \mathrm{MgCl}_{2}\) and \(\mathrm{NaCl}\), crystals of pure \(\mathrm{NaCl}\) seperate out. Calcium and magnesium chloride being more soluble than \(\mathrm{NaCl}\), remain in solution.