How is hydrogen prepared in the laboratory by combining zinc and hydrochloric acid?

When zinc is combined with hydrochloric acid in a laboratory setting, the reaction leads to the production of hydrogen gas. The key aspect of this reaction is that zinc displaces the hydrogen ions present in hydrochloric acid, which is a typical reaction for metals that are more reactive than hydrogen.

The reaction can be summarized by the following chemical equation:

[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \uparrow ]

In this equation, zinc (Zn) reacts with hydrochloric acid (HCl) to produce zinc chloride (ZnCl₂) and hydrogen gas (H₂). During this process, the zinc replaces the hydrogen ions (H⁺) in the hydrochloric acid, enabling the release of hydrogen gas, which can be observed as bubbles forming in the solution.

This displacement reaction demonstrates how a more reactive metal can replace a less reactive element in a compound, which is fundamental in understanding single replacement reactions in chemistry. Thus, the correct answer accurately describes the mechanism of hydrogen production in this context.