With respect to the laboratory preparation of hydrochloric acid answer the following question :
Name the substance A and give its use .

Explanation

To answer the question regarding the laboratory preparation of hydrochloric acid, we need to identify substance A and its use.

### Step-by-Step Solution:

1. **Identify Substance A**: In the laboratory preparation of hydrochloric acid (HCl), the substance A is concentrated sulfuric acid (H₂SO₄).

2. **Explain the Reaction**: The reaction involves the interaction of sodium chloride (NaCl) with concentrated sulfuric acid. The chemical reaction can be represented as:
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