Which acid is used in the preparations of Hydrogen Chloride gas?

Solution:

Concentrated Sulfuric acid (H₂SO₄)

(i) Sodium chloride is treated with strong sulphuric acid to produce hydrogen chloride gas. To remove moisture, the HCl gas is delivered through a drying agent, where concentrated sulphuric acid also acts as a dehydrating agent.

(ii) NaCl+H₂​SO₄​→NaHSO₄​+HCl_(g)