(i) What must be added to sodium chloride to obtain hydrogen chloride?
(ii) Write the equation for the reaction which takes place in (i) above.
(iii) What would you observe when hydrogen chloride mixes with ammonia?

Explanation

### Step-by-Step Solution:

**(i)** To obtain hydrogen chloride (HCl) from sodium chloride (NaCl), you must add sulfuric acid (H₂SO₄) to sodium chloride.

**(ii)** The chemical equation for the reaction that takes place when sodium chloride reacts with sulfuric acid is:
\[ \text{NaCl (s)} + \text{H}_2\text{SO}_4 (l) \rightarrow \text{NaHSO}_4 (s) + \text{HCl (g)} \]
In this reaction, sodium chloride reacts with sulfuric acid to produce sodium hydrogen sulfate (NaHSO₄) and hydrogen chloride gas (HCl).

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