NaCI contains impurities of some other salts like ${{Na}{2}}$${{SO}{4}}$, Mg${{Cl}_{2}}$ etc., which absorb water vapour from air, thus making it wet.
NaCI contains impurities of some other salts like ${{Na}{2}}$${{SO}{4}}$, Mg${{Cl}_{2}}$ etc., which absorb water vapour from air, thus making it wet.