..................... And .... are used as reactants in the laboratory preparation of hydrogen

Answer

To answer the question about the reactants used in the laboratory preparation of hydrogen, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reaction**: The laboratory preparation of hydrogen typically involves a reaction between a metal and an acid.

2. **Select the Metal**: One common metal used in this reaction is zinc. Zinc is often used because it reacts readily with acids to produce hydrogen gas.

3. **Select the Acid**: The acid commonly used in this reaction is hydrochloric acid (HCl), specifically dilute hydrochloric acid.

4. **Write the Chemical Equation**: The reaction can be represented by the following balanced chemical equation:
\[ \text{Zn (s)} + 2 \text{HCl (aq)} \rightarrow \text{ZnCl}_2 (aq) + \text{H}_2 (g) \]
In this equation, zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.

5. **Conclude the Reactants**: Therefore, the reactants used in the laboratory preparation of hydrogen are zinc granules and dilute hydrochloric acid.

### Final Answer:
Zinc granules and dilute hydrochloric acid are used as reactants in the laboratory preparation of hydrogen.

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